It depends a bit on the bike, to me. Also, it depends a little on how aggressive you want to be and how much skill you have to be aggressive. For example, the slipper clutches. At the local track there are two corners in which the slipper clutch allows me to enter them much hotter and much deeper, and it is really fun!!! However, the three other bikes that I have taken to the track didn't need a slipper clutch, because I approached the same corners in a different manner (those bikes couldn't have done the same thing). I think traction control would be amazing for a trackbike, or a literbike ridden as a commuter. Beyond that, decent throttle control takes care of everything. ABS, that would be great on a commuter bike. It has been proven to stop shorter and safer. However, it wouldn't want it on any other bike. Air shifters (or the like) would be incredibly fun if you were competing on a high HP bike, but otherwise you would never use it (other than for being silly). And, steering stabilizers aren't as necessary as they used to be. I have only had one semi-tankslapper in 2 years on my ZX10, and it was a really weird situation (I was glad it was there).
So, to me, it depends a lot upon your use of the bike. However, I don't want anyone to have this stuff (except the commuters) until they have learned to ride a bike well without them (or they might do something stupid).