I can't speak for the Egyptologists, but what they say (the inscriptions, not Egyptologists) is in and of itself not very interesting. For the most part, they are the kind of inscription that people from all over the world seem to leave at various places as if following some primal urge to mark a certain place as having been visited by them, i.e., tourists scratching their names on the walls of some attraction, or maybe in modern times, shoot a selfie with the attraction in the background.

Anyway, before I digress too far along ways I'm not equipped to go, let me return to the inscriptions at hand. The grafitti material from the Valley of Kings near Diospolis Magna/Thebai/Thebes has been edited and published by Juiles Baillet in Inscriptions Grecques et Latines des tombeaux des rois ou syringes à Thèbes, (Kairo 1925-1926) of which the first tome is on archive.org ‌[here](https://ia801304.us.archive.org/23/items/MIFAO42/MIFAO%2042%20Baillet,%20Jules%20-%20Inscriptions%20grecques%20et%20latines%20des%20tombeaux%20des%20rois%20ou%20syringes%20%C3%A0%20Th%C3%A8bes%20(1926)%20LR.pdf), so you can have a look yourself - there are lots of plates and tables in the back section.

These grafitti were painted in red or black ink, or scratched directly into the surface in a manner that would probably be detrimental to your health should you try it today, but those were simpler times in that regard. Most of the inscriptions are in Greek, some (27) are in Latin, others are in Demotic; almost all in prose, some in verse. As you said, most of them were found in KV 9, the tomb of Rameses V/VI. However, at Roman times, this tomb was identified as the tomb of Memnon, the mythical king of Ethiopia to whom also were attributed the famed colossi of Memnon.

The majority of these inscriptions is very simple: most of them consist only of one or several names, sometimes with their titles or their origin, sometimes with a bit more information. To give you an idea, here are a few of them.

Most of them are simply a names some singular Greek or grecized names, like Rufus, Eunikos, Aristarchus, others are full Roman names like M(arcus) Porcius Marcellus. Many were there alone, others came with their friends or family or in greater groups; some added their origin, such as Origenes from Sidon (Ὠριγένης / Σε̣ι̣δ̣ωνίς; IGLTheben 107). Others were a bit more elaborate, such as 'Euphranor, son of Philon from Rhodes, (was here) under Ptolemy son of Ptolemy in his 7th year, in the month of Panémos' (Εὐφράνωρ Φίλωνος Ῥοδιος / ἐπὶ Πτολεμαίου τοῦ Πτολεμ[αίο]υ (ἔτους) ζʹ, / μηνὸς Πανήμου; IGLTheben 30). Dates, however, are only rarely given.

Another group of inscriptions is a little more eloquent. For the Greek ones, this is most often with an ἥκω appended to the name, I have been here, I have come (i.e. 'X was here'), like Seleukos (Σέλευκος / ἥκω; IGLTheben 649b) which can simply be read as 'Seleukos was here'.

For the Latin speakers, Macus Laetus marked the walls with his simple 'Marcus Laetus was here' (M[arc]us Laetus hic fuit; IGLTheben 978). There are well over a hundred of these. Some also comment on the quality of there experience, like Kephalon. 'I have come here, and I am doing/being well' (Κεφάλω/ν ἥκω{ι} ὑ/γιαίνων; IGLTheben 330). Others simply write scripsi, I have written (this) (like IGLTheben 1409).

Others also comment on the nature of their experience. Most often with verbs such as miror or θαυμάζω, to wonder, marvel at. In the simplest form like this, 'I, Solon, have marveled (at this tomb)' (Σόλων / ἐθαύμασα; IGLTheben 94). One of the more illustrious guests of the tomb was Marcus Ulpius Antiochianus Pulcher, a military tribune, who scratched on the wall: "Marcus Ulpius Antiochianus Pulcher, from Emesa, military tribune of the 7th twin-Legion, the lucky one, and the 3rd Augustan; I have happily inspected (this) when Apronianus and Paulo for the second time were consuls on the day before the Ides of November (12th November 168), with Epictetus, actor (maybe a local guide?)" ([M(arcus)] Ulpius Antiochianus / Pulcher domo Hemesa / tribunus mil(itum) leg(ionum) VII Gem(inae) Fel(icis) / et III Aug(ustae) inspexi Apronia/no et Paullo II co(nsulibus) pr(idie) Idus / Novembres feliciter / cum Epicteto actori; IGLTheben 1448).

For some, the experience was so good that they visited a second time, such as Philaster (Φιλάστριος τὸ βʹ ἱστόρησα; IGLTheben 745c).

Ianuarius, primus pilus (first centurion of a legion), remarks 'I have seen and marvelled at the place', vidi et miravi locum (IGLTheben 1585), and apparently he was so enamored by the place that he repeated this statemend in the same phrase in another place as well (IGLTheben 1504). And maybe he liked it so much that he brought his daughter the next time (this is purely conjecture by me, but it does make for a good story, try to prove me wrong): 'Ianuarius, primus pilus, I have seen and admired the place with my daughter Ianuaria, farewell, everyone!' (Ianuarius p(rimi)p(ilaris) vidi et miravi / locu(m) cum filia mea Ianuaria / valete omnes; IGLTheben 468).

Mauricius, an equestrian and dux writes vidi et miratus sum, I have seen and been amazed (IGLTheben 1423).

A similar eloquent visitor wrote: 'Apollophanes, son of Ierax from Lykopolis, after I had come I have inspected and I have marveled at (the tomb), I have come in the 7th year of Antoninus (i.e. Pius), on the 25th of the month of Tybi (21st January 144 Julian/20th January 144 Gregorian)' (Ἀπολλο/φάνης Ἱ/έρακος / Λυκοπολ(ίτης) / ἰδὼν ἱσ/τό/ρη/σα / [ἐθαύ(?)]/[μ]α/σα /ἥκ/ω/ν /(ἔτους) ζʹ Ἀντω/νίνου, Τυβὶ κεʹ; IGLTheben 193)

Other illustrious visitors included officials from the Roman administration of Egypt, such as the prefect of Egypt, Sulpicius Similis (IGLTheben 1412).

These inscriptions continue into the 3rd century, and into Christian times, where another illustrious visitor is recorded: 'Claudius Bassus alias Himerios, the most distiguished Katholikos of Egypt, from Bithynion/Claudiopolis, I have inspected this, with my wife Aste' (Κλαύδιος / Βάσσος ὁ καὶ Ἱμέριος, / ὁ διασημότατος / καθολικὸς Αἰγύπτου, / Βειθυνός, ἱστόρησα / μετὰ τῆς / γαμετῆς / μου Ἄστης; IGLTheben 1247). What is interesting is that he also left the same inscription (IGR I, 5 1215) on one of the colossi of Memnon which where also at Thebes and which also contain lots of these inscriptions.

All these are just some examples, as you said, the whole corpus is ~2100 inscriptions, and there are also some rather long ones, prayers, invocations of gods/goddesses or Jesus and their good will, philosophical remarks (one group of visitors seems to have included neoplatonic philosophers who might have imagined themselves close to their master at this place) or are simply greetings or well-wishings for other persons.

But what most of these have in common is that they are simple statements of the presence or visit of a person or group of persons. This is what tourists have always done until today, so to close the circle, this is what most of these inscriptions have been about. They were made by tourists, who visited the famous tombs (syringes) in the Valley of Kings, such as the tomb KV 9 misattributed to mythical Memnon. In fact, the already mentioned colossi of Memnon had been one of the main attractions, but they seem to have lost that position to the tombs in the times of Septimius Severus. Strabon, who had visited the Valley himself, already had called them 'worth seeing' (θέας ἄξιαι, Strab. 17,1, 46), and Egypt, and especially Thebes, had become a prime target for tourists of Antiquity who had the best opportunities to visit the remnants of Old Egypt.

This is one of the big values of these inscriptions: they are proof of a non-neglible amount of tourism in antiquity, from singular visitors to groups, and with visitors from cities as far away as Marseille to Persia in the East and the Black Sea in the North. So they illuminate more of the history of Egypt in classical and late Antiquity, and of the Empire in general regarding tourism and mobility of people. This is just my perspective as a Latin epigraphist who never really cared that much for Egypt (since I did never do much in the area), so an Egyptologist or someone specializing in Roman Egypt would probably be able to give you a wholly different answer to this question. Adam Lukaszewicz has written in a survey about these inscriptions that "their respective location may shed additional light on the visiting conditions of the time", but that work still seems to be forthcoming so it might be some time until these inscriptions are evalued from a modern perspective.

What personally interests me most is that here we have a long list of names, which is in and of itself interesting from an onomastiv point of view, and since these names contain important members of the elite of Roman Egypt as well as lots of names from people who came from far abroad, this is a valuable resource in itself for research into issues of names and mobility.

I hope that my answer was a bit helpful, I am neither an Egyptologist nor a specialist on Roman Egypt, but I had read about these inscriptions before, so this was my epigraphers perspective on them. From a human point of view, I find this whole collection simply amazing, since this is a form of epigraphic practice that has remained a constant for milennia in one form of another, and to see that people from 2000 years ago travelled to Egypt and inscribed their name into the walls of a tomb just to prove that they had been there (to what audience? and why?) just like people do today (and I did so myself - not on something priceless as this, but still, in a form) is something incredibly cool.