If I wanted to make an iPhone game like this one (ignoring the multiplayer functionality):
http://itunes.apple.com/us/app/scramble-with-friends-free/id485084223?mt=8
Would it be wise to use cocos2d? Or would that be overkill? Or is another engine better?
No, I think that Cocos2D would be a great choice, even if you don’t need all of it now, you can build on top of it later. Cocos2D is just a wrapper for a 2D game and any board game is such. If you’re dealing with a lot of animation it’s probably a good choice, otherwise if it is mostly static and really simple UIKit and CoreGraphics may be a better bet.