Any change in the original finish can affect the collector value of any gun. I would think changing the "finishing effect" on a stainless gun wouldnt affect it as much as rebluing a carbon steel gun.
I have bead blasted quite a few of my stainless guns, but I was not worried much about value. They turned out great as far as Im concerned. Here are some of the after pics. The 625 already had a matte finish, but it was rough. If you do bead blast a gun that has lazer engraving or markings, cover them because the blasting can lighten or completely remove them.
686
686
625
65
66