There was an article in View Camera magazine some time ago which reviewed the new ArtCare mounting board. In the course of their tests, they compared the permanance of prints both hinged and dry-mounted. The dry-mounted prints showed substantially less degradation due to aging and chemical contamintation. I feel that, as far as permanance is concerned, dry-mounting is the way to go, especially for art photos where the presentation, placement on the mat board and overmatting is an integral part of the artwork.
I use the Seal "BufferMount" (formerly "ArchivalMount" low-temperature mounting tissue. It is also removable by heat. I routinely mount prints that have been selenium toned, many to completeion, and have never noticed a change in image color, or damage of any kind.