It appears darkmoon cards are going to keep their price points up for another darkmoon faire or two. I still see cards above 1k gold consistently and decks, not trinkets are being sold readily at 10k plus. I had originally decided to get out of the game and pursue greener pastures in the gem market, and while the gem market is standing strong there's no reason not to be in the darkmoon market with herb and volatile prices so cheap on most servers.
There's a niche secondary market for these cards/trinkets as well. every time you turn them in you get rep towards the darkmoon fair which is required for the achievement Insane in the Membrane it's quite intense and requires a lot of reps all around, and has even been nerfed since wrath but is still quite the feat and allows you to dawn the title "The Insane" which is befitting of most people that spend 50-100k gold on a single rep from an achievement that requires many.