Soul CD's have little resale value, save for the odd few that are in demand, believe me - I spent nearly 30 years amassing a very hefty collection of new releases, many rare indie ones which can be seen for crazy money from chancers on the likes of Amazon or Discogs or wherever, but honestly, nobody wants them. I sold mine because of both storage space (not having a garage in the new house to put them) and never actually playing or looking at them any more.
I put a load of discogs, tried to get hefty prices on a few I thought I could and failed miserably on most of them, I sold them eventually in a couple of jobs lots, at a fraction of what they cost me.
I've also been doing CD cover designs for 20 years now and have seen it all decline to the point where I rarely do a cover for an artist album, and even the compilation/reissues are struggling miserably with sales these days unfortunately, though the resurgence of vinyl has seen a bit of an upturn in fortunes, though no to the extent people are going to get rich off it.
Sadly I think the end of the CD, as much as I've tried to kid myself for years now, is definitely in sight and if you're hanging onto a CD collection in the hope of making a good few quid, honestly, think again!
Cheers
Roger