If I was Apple I would take on Nintendo's 3DS, the iPod touch costs only a little more and offers so much more than the 3DS. Not that the touch should be marketed just for kids though, it does so much more than just educational apps so they need to market to adults who don't want to pay the high price of a data plan. But the educational apps are there, and Nintendo doesn't have them, they only have their franchise games which cost $40 each really.
From personal experience the iPT also grows with kids, while kids just outgrow Nintendo systems eventually. With the iPT you can simply install new apps when the old ones are outgrown.
I don't think taking on the Vita is a bad idea but really that is a no brainer for me, I would pick the iPT over the Vita any day. Again, the iPT does everything the Vita does and more.
IMO if you have a touch its the only portable device you need unless you travel a ton. Since I am not a heavy traveller it suits my needs just fine. Might need to keep a portable USB battery on hand though. The other devices simply can't live up to the touch for me, bored with games, you can read books on the touch or listen to music, it simply does everything.