Oh, definitely leave well enough alone. Mine was not framed well – when the conservation place took it apart, it was obvious it had been done by an amateur. In addition, part of the sampler was folded under in order to fit the frame, and the glass was not UV-protected. If your sampler is in decent shape and protected, it’s probably as good as you’re going to get it.
Also, if it’s framed, it generally doesn’t get dirty.