Medieval Scandinavians were hardly vain, but they did have pride in appearance; we know from sagas that having clean hair and clothes was important, and the most common archaeological finds in Scandinavian graves at this time are combs. There's linguistic evidence, too - the Icelandic name for Saturday is Laugardagur, literally washing-day.

As far as clothing goes, there were individuals like Olafr pai (Olaf the peacock) who were renowned for wearing brightly coloured clothing.

As far as vikings are concerned, they were raiders and warriors, so of course appearance was important; if you're wealthy from plunder and fighting, you want to show it. Egill in his heyday is described (in the eponymous Egils saga) as wearing all black clothing with a scarlet-lined cloak, for example. There are dozens of other descriptions in other sagas of the clothing that successful vikings wore, and it is usually all finery.

Steven Ashby has just published a brilliant little book on the subject of (fanfare please) Viking-Age combs! He opens his chapter on comb uses with two very relevant quotes.

First, the familiar Ibn Fadlan, an Arab traveler who wrote about the Viking Rus' (922):

Every day they must wash their faces and heads and this they do in the dirtiest and filthiest fashion possible to wit, every morning a girl servant brings a great basin of water; she offers this to her master and he washes his hands and face and his hair - he washes it and combs it out with a comb in the water; then he blows his nose and spits into the basin. When he has finished, the servant carries the basin to the next person, who does likewise. She carries the basin thus to all the household in turn, and each blows his nose, spits, and washes his face and hair in it.

He follows this with a letter by Alcuin, an English churchman making it big in Charlemagne's court, to the Northumbrian King Æthelred, whose kingdom was suffering from some of the earliest viking raids (790s). Apparently Æthelred had been something of an aficionado for the Scandinavian style:

Consider the luxurious dress, hair and behaviour of leaders and people. See how you have wanted to copy the pagan way of cutting hair and beards. Are not these the people whose terror threatens us, yet you want to copy their hair?

Ashby shows us that everywhere the vikings went, they took their combs with them. Many of them were even buried with their combs, clutching them in their hands or hanging them around their necks. There was even a cottage industry producing novelty-sized combs to be placed in your funerary urn if you decided to be cremated.

Ashby's work is especially important because it lets us see what how males tended to their appearance. Archaeologists and the people who put together museums most often focus on fancy metal objects, but the metal jewelry that survives was typically feminine. Since viking is a word that translates roughly to "pirate," these feminine objects don't help us much to imagine what the viking raiders really looked like. By showing us how Viking-Age males tended to their appearance with combs, Ashby adds another dimension to our understanding of these warriors from the north.

So in answer to your question: Ashby shows us a bit about what the vikings actually did. Alcuin seems to think it was vanity. Ibn Fadlan was decidedly unimpressed. But Alcuin was a churchman who valued austerity, and Ibn Fadlan was a diplomat for the most dazzling empire of his day. Were the vikings really vain? I guess that's up to you: Are you more of an Alcuin? Or more an Ibn Fadlan?

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