Here is the way I think of it.
Do better specs = fun?
No.
It's all about the games.
Better specs can lead to games that may have more features which could potentially be fun, but that doesn't necessarily mean they are going to be fun. (ex. Sonic 06, Final Fantasy XIII)
It also depends on what kind of gamer you are.
Do you want to play Mario, Kirby, Smash Bros, Zelda, etc ? -> Buy a Wii. (They are dirt cheap on craigslist)
If you want better graphics and more "hardcore" games then buy a vita.
Vita doesn't really have any upcoming titles, while maintaining a rather small library of games
Wii is basically dead in terms of releases but has a huge library, although a lot of games are pretty bad in terms of quality.
I would go with the Wii though because they are relatively cheap and it has quite a library. You are bound to like a couple of games.
Vita doesn't really have a system selling game yet because a lot of the first party games don't live up to their console versions.