Remember too, that many collectors collect, not for the value of a poster, but for the aesthetics of the poster and the film history it represents. Those types will not be as concerned about snipes or stamps (unless they were placed over some key art, a face important credit etc).
And many will keep the snipes in place, to allow the history of that (used & displayed) poster to shine thru. Much like snipes attached to to the tops of Belgian posters or Belgian tax stamps. Again, unless intrusive in some way, I would choose to keep both in place, every single time.