I only see 2 options here: If the PS4 games are made to really integrate the Vita into the gameplay, but I don't have the Vita, will I be missing half the game because I am playing an incomplete version with just the basic controller? In this case, I could be forced to buy the Vita just to fully utilize the console and games I already have.
On the other hand, if the games are created to work fine without the Vita, I would just get access to throw-away gimmicks that probably won't justify buying the handheld console (just like it happened with the GameBoy Advance and Game Cube... hooking them up was a waste of time and money)
In the case of WiiU, the tablet is part of the console, so the games *should* be optimized to use it. I'd say It's a safe bet that at least first party Nintendo games will be making a good use of it.