In the end, I found this bloom shader writeup on GameRendering.com to be the most useful. It presented how to do a Gaussian blur plainly and clearly without the math upon which it is based (which I usually like, but it was distracting me from getting results).
So, this morning I had a nice bloom glow. But now that I had it, I wanted more: since this game is intended to be synaesthetic, I wanted the bloom to pulse to the beat. It took some time to figure out what intensity and speed looked good, but I quite like the results.
I also made the power pellets blink.
The drum track now fades to its target volume instead of jumping there directly. At least, most of the time. There are occasional instances when it seems to jump to max volume instead of ramping up; I'm not sure whether this is a real bug or a "trick of the ear." I need to mute the other tracks and test it further.
Incidentally, I noticed while preparing to make this video that Fraps reported a frame rate of 95 in the menu, and 29 while playing the game (running at 1290 x 720 windowed). I'm working on an Intel Core2 Duo 3GHz with 4 GB ram and a NVidia 9600 GT. Not the top of the line anymore, I know, but I expect my rendering code is horribly inefficient. Maybe I can optimize it to improve performance at some point.
I just realized I may need to remodel the player model. It chomps while moving, but more often than not the model is facing (obliquely) away from the camera. I guess I should give it a bigger mouth or have it open wider.