David,
I don't have such a dense star field but I have a bunch of largish stars that I'd like to de-emphasise so that my galaxies (NGC 4038 and NGC 4039) stand out more. I have devised many clever, but ultimately unsuccessful ways to do this so far
I can achieve the desired result but that usually causes some other less desirable side-effect. Still, I'm learning lots of new tricks for combining masks in PixelMath. I have a feeling I might finally get close with another night of playing... I could get there by blending a couple of different versions of the image in Photoshop but I'd rather not "cheat" if I can avoid it.
Cheers,
Rick.