I 2nd this request.
I personally wouldnt particles to become *too complex*, I just wish more parameters supported negative numbers. For instance, you cant create a particle with a negative speed. While im sure this normally would not be necessary (if they all spawned at the same point it would appear exactly as it would as with positive speed, just transformed 180 degrees), if you spawn your particles at random spots then you would end up with an 'implosion' effect of sorts. But, particles cant have negative speeds, so you would need to simulate this kind of effect yourself.
And if this functionality were added, then maybe a negative fade out time could become a fade in time?