Are roof tiles derived from Ming period architecture widespread and typically of low value?
The "trade" price for a "fairly genuine" Ming architectural piece is about $ 500-800. Figures with horses are the most popular, I would say. With fairly genuine I mean - with at least some age or, accepted by the trade as "old". This is very vauge, I know. That is because it is so hard to tell genuine Ming period tiles from later replacements. The prices asked does not merit anybody making TL tests on them either, since the tests are about the same as the price for the tile. Most probably the genuine ones are also so battered that not many would like them.
Replacements are by definition made similar to the originals, and as long as the roof was there, there was also a need for a tile.
I don't know how to separate Ming from, lets say, 19th century other than looking carefully at the style, the color of the glaze, for crackles and damages, and .. hope for the best