Figure'd I'd reply to both because reasons.
Alright relevance, in 4 Swords he was also the main villain, which I think would make him pretty important, and in Adventures he was the secondary villain, only second to Ganon, which reminds me of another fabulous villain I know.
And you can't even say Nintendo forgot about his games or don't care, because they've re-released his games and even made a remake of one.
Now for popularity, Vaati's still incredibly popular as a Zelda character, and is still pretty popular as a Smash contender. Heck, he's got a pretty big following under him that's been wanting him in another game for quite some time now.
And finally deservance (if that's even a word), I'd add his popularity and relevance to his deservence along with being an incredibly unique character and being the 2nd most reoccuring villain only to Ganondorf himself.
So, did I do good guys?