The only problem I have with peripherals like that is that they are so bulky and a pain to store, like the !@#$in' Rock Band drums!! A friend of mine was moving and had no room for his Rock Band instruments so he tried to bring them to EB Games and maybe get a few bucks for them but the store didn't even want them, so he ended up yelling out "Rock Band stuff, $10!" and got kicked out of the mall, haha.
Anyways, all that to say that stuff like the bongos and plastic guitars are fine and novel, but once you're done with them, they suck to keep around.