Yup, there is also an issue with all 3 particle generators when you add an effect to only one of them. Apparently all 3 generators gets affected by the effect configured in only 1. Go ahead and try it; you'll notice that only 1 of the particles generators will work with the effect applied while the other 2 particle generatores are completely disabled.

I've tried applying several effects, but the result is the same.

Regarding the long delay in getting the screen filled with those particles; I think that this could work if you increase the timescale as you mention, and once the first particle reaches the destroy event (or the bottom of the screen) immediately drop the timescale speed down to a reasonable scrolling speed...., but this is only a general idea since I haven't tried this.

Playing around with particle effect, i've managed to make this simple top-down starfield by using 3 particle generators.

Maybe this can be done with a single particle generator, but I couldn't find the correct values.

Here is the link to the CAB file:

http://www.2shared.com/file/5834524/6ed11b1a/Starfield.html

Note that the download link to the file is located at the bottom right section of the site.