Funny really - imagine if someone found the elusive Metropolis US one sheet, unrestored in its original state?
What's the betting the finder would have it backed!?
My bet is that is would remain unbacked - like the Mummy 3-sheet, the Bride of Frankenstein 1-sheets, the best Mummy 1-sheet, etc., etc.
In almost every case where a nice* copy of a key poster has been discovered, the purchaser wisely chooses to keep it unrestored.
*nice copy being the key word, a lesser condition copy will almost always be restored.
I only see the results that Bruce posted here, so am unsure as to which posters you believe are bringing record prices because they are backed (and this may well be true for average pieces in the $300-1000 range), but we just saw a record price for a 50ft Woman (nearly 50% more than the copy Heritage just sold about a month ago) and where there was strong underbidding, you have to believe that is was because of the condition and the fact it was unrestored.
Similar for the Creature From the Black Lagoon that was posted - an average/strong price for a linen-backed copy. But Heritage has sold three different unbacked copies for $20K plus.
A top condition unrestored poster from an in-demand title will 99 out of a 100 times bring more than a lesser condition copy that has been linenbacked.
I think where people are getting is confused is seeing posters that were in C-4/5 shape being restored to apparent C-9s and bringing more than an unrestored C7 or something.
Yes, a prior C5 that has been restored will bring more than an unrestored C5 99 out of 100 times.
And it should.