One of the few brands that warrants the investment in rebuilding. It is early, though, and people shy away from pre 1920 pianos. If it's a screw-stringer, it's probably more of a curiosity than a usable piano. Screw-stringers, if you're not familiar, was a method of tuning developed by Mason & Hamlin, using bolts and nuts to tune the instrument rather than a pin-block and friction pins. They tuning was very-very stable, but the heads of the tuning pins were an odd shape and they rotated in the opposite direction of normal tuning (counter-clockwise, rather than clockwise).
In good shape your piano could sell for $2,500 - $3,000 ... but it's got to be truly in good shape, not just an owner's estimation of good.
Mason's remain my favorite piano. I have played a number of model 50 uprights that are far superior to 6' grand pianos, even from other well known makers.
... and I've got a 1969 B (Yeah, I know those were the Aeolian-American years.)