probably none i usually end up selling them or giving them away, either that or they break, they'll probably get the new consoles and games during their generations...I'll just have an emulator for everything oldschool, unless I use the backwards compatability on the future-gen. systems :P
but honestly in my opinion, they probably won't care, or won't play the old stuff as much since technology eventually improves, but I hope they at least try Mario and Tetris