So I spent a bit more time trying to puzzle out the shaders in Neon Galaxy. aesir_of_doom mentioned Defcon, by Introversion, and I was all like, "say, yeah, that game had a nice clean vector look..." So I booted it up and had a look.
(As a digression, I don't actually play Introversion games that much, because they're mostly strategy games and I'm just not into that genre. But I've bought just about everything they've made because their games are so damn cool. I guess I'm supporting them in the hope that one of their future products will be in a genre I actually like, which is kind of nuts but there you go. Crossing my fingers for Subversion, whatever it turns out to be!)
Anywho: Yup, Defcon sure is pretty and while I wouldn't say I want to exactly copy them, that's generally the look I'm going for. So in the hopes of figuring out their shader tricks I studied the game a bit more... zoomed in on the map while the AIs fought out their thermonuclear war... noticed that the nice glow around the continent edges gets all blocky at the highest zoom... downloaded a mod or two that adds custom maps, just to examine the source data and be sure... Introversion, you clever bastards. All you did was use a paint program to create a map with the precise effects you wanted, and load it as a texture. Even the funky way units blur when selected is just because the "selected item" texture is deliberately blurry. There are no special shader effects at all!
So I was just gonna shrug and get on with things, but then I had to stop and think. Maybe I'm just making this too complicated? Maybe I should just render me some glows after all. I can't pregenerate the map since the environments in Neon Galaxy are completely dynamic, but I can certainly whip up a few gradient textures and use them to paint the world as needed. And so:
A gradient adds some subtle texture to the room shapes (possibly too subtle now that I look at it on a cheap monitor, but anyway.) The vector lines are brighter at the tips. I let OpenGL do the anti-aliasing for me. And really, the result is fine. I'll keep tweaking it, as I want better glows on the stars and I also want a sort of superbright effect for a few specific game elements such as enemy fire, but yeah, I think it'll do. The next step is to have some player and enemy models that are actually colorful and attractive!