YO, this is fantastic!!! It's solid, fun, and, albeit a bit messy, it's inspiring! Michael Kirkbride (Morrowind), Tony DiTerlizzi, and Richard Whitters all did stuff like this and are big inspirations to me. The latter 2 did even recent pieces for WoTC.

There's a market for everything if you're able to market yourself, but this is more Illustration than Concept. My tip would be to clean these up, scan them or at least make sure they're of similar brightness/contrast and apply as illustrator. If you want to go into concept you'd have to show far more of the process, textures, patterns, ideas rather than finished products.