Oh, and taking some more inspiration from Rayman Origins; how about implementing wall jumps in JJ2+? Maybe even make it require a certain speed to work, or link the strength of the wall jump with the player's speed. It would give level designers another tool to reward speed.

Another factor that I imagine might be at play in this issue is the fact that Jazz is up to top speed in, like, 2 frames. Getting hurt or losing your momentum otherwise is cheap as you can get back to full speed with little effort. If acceleration would be lower, interesting things could be done with speed in a level design sense; for example, platforms could be made so small that players would not have enough room to achieve full speed, which would limit the reach of their jumps, et cetera. I don't know how feasible changing this is engine-wise, though, maybe all there is in the game code is a binary switch between "slow" and "running" rather than a discrete "speed" value.