I have all of the peripherals and all of the pro instruments. I play them all, and I wouldn't give up a single one of them. Pro instruments to learn how to play the real deal. legacy for just the pure fun and challenge of it, and blitz when I don't want to work hard at playing. The dlc is to die for.
HMX has done a fantastic job of meeting the needs of pretty much anyone who wants to Rock Out in some form or fashion. I don't think I could ask for anything more.
I just want to be able to keep playing and have new challenges and goals along the way...hence...the need for RB4, as well as the ability to get replacement instruments when necessary. With the kind of investment people have made in this particular game, it seems like a reasonable expectation. but that's just me.