Dry plates are basically just sheet film on a funny substrate; anything you can do with a 4x5 sheet you can do with a 4x5 plate (except fold it, I guess). I can't think of any reason that the negative being on a plate would affect the blacks in the final print. You might be seeing contact prints, which seem to have a certain visual "pop" all their own, but probably spectacular blacks in a print are just a sign of a printer who's getting really spectacular blacks.

There are plate cameras down to at least 645 format, and I would kind of expect that people wanted to enlarge those images most of the time, but contact prints and plates are a natural match because the plate can be its own printing frame, holding the paper flat and the emulsion in contact. For enlarging I think it'd be easier to just use sheet film.

Wet plate, I know nothing about. I think the plates are wet.

-NT