When I said I was going to redo this I wasn't entirely sure that I believed myself. But tonight, having no other source of amusement, I started adding some color to it.
I'm going to do something different (but still equally worthy-to-be-airbrushed-on-the-side-of-a-van) to the background. I don't quite know what yet but it'll be awful, I'm sure.
No particular part of this is done yet... I've just been picking here and there at values. I'm pleasantly surprised with how much better I've become since that original post was done back in December!