If you own a PlayStation 3 you're probably already familiar with half (if not all) of the current Vita library, and that alone constitutes a pretty good reason to purchase one. Games like Uncharted: Golden Abyss, Wipeout 2048, Rayman: Origins, and Little Big Planet (to name a few) are really great in their own right, I personally enjoyed Rayman: Origins the most which, for me, was a lot more enjoyable than it's console counterparts.
Other titles like Gravity Rush, Persona 4 The Golden and whatnot are must plays. I might actually go as far as saying that you would be missing out if you did not get a Vita.
While its library isn't that huge right now, it's getting a lot bigger, and with E3 coming up soon, who knows what else us Vita gamers will get!