Anyone putting extra value on any board because it's undumped and therefore can be used to "extort money from mame people" are flat out sick people with a diseased brain and need to see a doctor. Preferably one from the 19th century bent on lobotomies.
I think half the people out there overcharging for undumped stuff are so stupid that they literally think everything dumped in mame is less rare than whatever undumped junk they have and the other half just see dollar signs and are so greedy the thought of giving something back to mame is not a serious thought.