No, not just between fast / slow
I just think there's a lot more we could be doing with foot expression besides volume swells and filter sweeps.
I have a Strymon Mobius on my live board, and I have one of those Mission EXP pedals to control parameters. And maybe the coolest thing about the Mobius (outside of the sound) is how you can map virtually any parameter to the Expression pedal and save it as part of your patches. I even had a phaser patch where rocking the expression pedal toggled the effect between being in front of the amp or being in the loop.
It's just that kind of flexibility makes you think a little bit... what about OD / Fuzz? I think I'd actually get some use out of a nice OD where I could easily control the level of gain with a treadle.