The better $$ for postcards is prior to the dates you quoted. I've peddled earlier Detroit RPPC's on eBay for tidy sums, depending on the subject.

I still have a tidy stack, but with the economy, most eBay sales are languishing, including PC's.
Trying to peddle a whole collection to a dealer, the most likely buyer, would call for a very hefty discount from already depressed values.