Thanks, @skullguzma, for both the tips on entering and final polish.
I already have a bunch of overlay layers in my piece... but the rules sound really strict about no using any photography, so I started getting really paranoid that my entry would be eliminated for something small like overlay layers of lens flares and stuff. So just to be on the super-extra-safe side, I'm repainting by hand the overlay lighting layers I've been using.
Maybe this will be useful for someone:
For the spotlights, I created straight lines first and then distorted them into place (adding some masks and such to fade them out.) Because straight lines are easier to create.
To create a lens flare, I created the straight lines first again, and then used 'Polar Coordinates to turn a straight bunch of lines into a radial bunch of lines. It takes a little experimentation to get it just the way you want it, but at least now I can get rid of the photo texture and say I painted it all by hand!
edit: I'm totally embarrassed. it's "POLAR," not "polor."