PS4 version worth picking up for $24 with GCU?
If you are looking for better graphics, or enhancements of any kind, you are gonna be disappointed, I really didn't notice much of a change. I think the framerate runs a little smoother, the same is true of the WiiU version too, but overall I think most people would be hard pressed to find a difference.
But yeah, it seems to work just as well as the PS3 version does (from what I played of it anyways, I don't actually own a PS4 yet lol). It's certainly a great game in it's own right and, stages aside, the fan service is incredible.
People complain about the online being dead on the PS4 version, and from what I saw that is more or less true, but this isn't CoD. You don't need nearly as many people to sustain a healthy online community IMO. I doubt you'll ever have trouble finding a match, though depending on how much you play you may become very familiar with certain opponents lol.
I am planning on getting this myself, but since I already own the vanilla version I am waiting for a cheap price, $20 or bust. Even if I had a PS4, I'd probably still go with the PS3 version just because it's livelier online but either version should do you fine. The game is certainly worth owning in one version or another, but I see no real advantage in "upgrading" from the PS3 to the PS4 version.
Just stay the hell away from the Vita version, unless that is literally the only system you own that can play it.
Hope that helps.