trimming the skirt is a great mod, in my experience. the most noticeable improvement is how the bike accellerates. it's much smoother.
as far as power goes, a smoother running engine has more power, but the top speed isn't increased by too much. you're basically just getting a better tuned engine.
as far as shaving the piston dome goes, that's a touchy situation. if you do it too much, you'll end up losing power. graham bell has a good report on that ( google "graham bell 2 stroke" to find it.)