Archaeology is accelerating. I was in the field for a little so i can share a few things.

Foremost though, remeber that Archaeology as you know it is a young tumultuous discipline. While the field of history traces its roots back to the ancient greeks, scientific archaeology is only about 200 years old. Second, the world is BIG, capital B. Searching all of it in a systematic way would be/is a monumental undertaking. As systems improve, more money is allocated for surveys, and governments offer more support, ever more will be found.

Ok, now some insights into technology and practice that is accelerating discovery. The big one is laser scanning/LIDAR and their cousins. Airborne systems are getting better at penetrating foliage all the time. This has lead to large scale discoveries in South America and other densely covered and difficult to survey areas. Some companies are also working on water penetrating versions to survey coast lines and map shallow shipwrecks.

Which brings me to the next area. Underwater remote sensing with sonar amd other tools. Most of the ocean floor remains unmapped at archaeological levels of resolution because its slow expensive work using a sensor that is only good for a track a few hundred meters wide at best. The ocean is truly vast on a scale a human almost can't comprehend, and we can only map it in strips a few meters wide at a time. Nevertheless, these tools are constantly improving and as time goes by and more surveys are completed an ever larger body of data exists.

Last, ground penetrating radar is also constantly improving. Its a powerful tool trained interpreters can use to locate buried sites. But it suffers from a even smaller width than sonar. Most GPR is only a few feet wide. This tool also is under investigation as an airborne device.

These are just a few examples, but the take away is that we've explored, really truly explored, much less of the Earth than you may realize.

I suppose it depends on what you mean by accelerating and decelerating. It’s a complicated question. I’d say the best answer to your question is probably both – but in reality it’s accelerating in a bit of a different direction.

u/LaserPoweredDeviltry is right that archaeology is a very young discipline and new technologies and methods are being developed – and borrowed – at a break-neck pace. Most of these bigger and fancier technologies deal with detecting new, promising sites, and most of the methods deal with extracting ever more fine-grained data out of sites. In that sense, things are accelerating – people often forget some archaeologists are still working today that were working before radiocarbon dating became a thing, or were at least educated before radiocarbon dating was a thing, and now we have things like x-ray diffraction, GIS technology, AMS, and isotopic analysis.

There’s one big caveat though: what’s decelerating and going to become much rarer is… Excavation. Legacy collections are going to be looked at with more frequency. There’s a growing realization in archaeology that we’re running out of space to put stuff. Like, people are storing it in their garages and living rooms waiting for something better, kind of thing. Mexico has almost no space left; same with some places in the US like Hawaii. Couple that with how quickly things are changing, and there’s a sense of “hurry up and wait” while new technology has its kinks worked out. You can only excavate a collection once, and unless you already have a very well-established reputation, you’re not likely to get the grant funding to go back to a site that didn’t produce much on a hunch that you missed something, so you need to make sure you get everything you can the first time around, and the last thing you want is to spend a bunch of money getting some new tech or hiring a specialist to work it that ends up not contributing anything relevant.

The flip side is that lab work is taking off and only looking better, and we’re learning things from artifacts we never really thought possible just a few decades ago. Residue analysis lets us figure out what was stored in pottery or what a lithic was used to cut, for example. One cool thing in my subfield – zooarchaeology, the study of animals in the archaeological record – is called zooMS – zooarchaeological mass spectrometry. One of the biggest issues we had, especially when working with early coastal sites like where I work, is that there was no good way to identify fish remains to anything but the most basic of levels – that is, that they come from fish. With mammals you can usually tell exactly what it is with any single bone if you know the time and area it’s from, but not so with fish. A fish vertebrae is pretty much a fish vertebrae, and could just as easily be from a Unless you were lucky and got a cranium or something you were pretty much stuck, and fish crania are very infrequent compared to the number of vertebrae. Now we can actually look at the collagen and analyze the protein signature the bones have to speciate them, which means we can actually tell if people were collecting nearshore fish or if they had the capability to reach pelagic fishing grounds. It may not sound like much, but it’s kind of a game changer if it ends up working out like it promises to. On top of that are newer isotopic ratio testing techniques, which can be used for shellfish to (unreliably at this point, though we’re working on it) date sites and features without needing something rarer like carbon, reconstruct past climate data, and even determine the season of harvest with theoretical resolution down to the month (some say day, but that requires immaculate preservation). Shellfish are everywhere at coastal sites, and sometimes make up entire hills, so being able to actually date them is a big deal. We can submit a bunch of them for testing instead of relying on one or two charcoal samples. So, in this way, archaeology is definitely accelerating. When you ask if it’s getting more or less exciting it depends on what excites you about archaeology; if it’s finding big forgotten cities and treasure troves in the jungle, probably less exciting. If you’re like me and love looking at middens for evidence of social development or seafaring capabilities, it’s like Christmas, and you’re dreaming of all the cool things you can discover now.

As for the related question, no, not really. There are some examples of models being used at a local level, but not on a global level. Model building is another new avenue of research for the more computer-literate archaeologists, and I remember hearing some models did a good job when used to predict where roman trade posts were located and actually finding one that was previously unknown, but it’s been a number of years since I heard about that so I don’t have more details. Not all archaeologists trust models just yet however; they’re as accurate as the algorithms that goes into them, and not all algorithms are created equal. That’s kind of a long, disorganized answer, but hopefully it helps.