First of all, let me kiss some butt first. Moho's particle system is awesome. Sprite based particles with quick render times! Come on! That's how the big boys have done things like realistic smoke for movies (up until now with liquids that is). And it looks great! Simple crowd animations in a 2d program!? Awesome. And the controls are simple enough for anyone (try to get a good fire animation out of Maya without knowing some programming, it's not easy).
That being said, I have some ideas for improvements on the particle engine:
1st and foremost, make the values in the particle layer keyable. You can get some amazing effects if you could just change the values on the emitter and it's particles.
2nd and this one would take some serious thought: I was thinking that simple particle fields would be an awesome addition to the Moho particle tool. Gravity, vortex, wind, etc (or maybe just a directional force tool that can push particles around). Now I'm certainly not expecting a full blown 3d particle system. I'm thinking just start small, as a particle enters a 2d screen space (user defined shape or circle,etc.) the force acts on the particle. You could even allow for alpha values defining the intensity of the force. Like I said it would take some serious thought.
Anyway, kudos on the kick butt system you've already got working for you! It really does make Moho stand out above the rest.
...Another question would be how it'd works with 3D Spaced particles... but definitely I'm sure LM must have a good/perfect solution for this