Yes restomods can indeed command substantial money, and even exceed the value of an original restoration of the same vehicle. I've seen it happen at auction.

I can't imagine that a swap to disc brakes would hurt the value, unless clearance issues forced you to alter the wheels & sizes. An easier job would be to just change to a dual master cylinder, but keep the drums. Because this is a safety modification, it's unlikely points would get lost in judging.