well Uhm i'm guessing you did something like: fill layer with black, then add noise, then image>adjustsments>level to get less stars. and then did a resize of a part of the stars, to make those bigger. If you do it like that, the chance is, when resized to much the stars are going to look like dirt(which isn't round) My idea is to use a brish for the bigger stars.
Choose a brush with hardness 0% and then change it to scatter, opacity jitter and size difference(dunno whatsit called exactly) I think that would make bigger stars better
But this is just a Pointer cuzz i really like how it looks now!!