So, after realizing that the intake that Buschur Racing sells is really nothing much more than the DSM eBay intake, I picked up one of those for $25 and got rid of the stock airbox. No noticable performance impact (as expected; even with a bit of tuning, an open-element air filter doesn't improve much on the stock Evo airbox), but I got out of it what I was after: I can now actually hear what's going on with the BOV (oh, sorry, "DV"; EvoM folks love to spend all day arguing over semantics, such as "blow-off valve" vs. "diverter valve"), and it became obvious that my part-throttle hesitation was happening just as the valve was fluttering. This was also the first time I noticed that I appear to have a metal Evo 9 MR valve; it's generally considered to be a decent upgrade over the stock plastic piece.
So, upgrades so far (that I know about) appear to be an AMS catback exhaust (with adapter to the stock cat), the metal MR BOV, the intake I just added, a reflash from some unknown vendor, and possibly an upgraded clutch (I still haven't had a chance to peek under there through the clutch fork boot to see if I can tell what it is).
I've started off with a disassembly of the flash that was on the car when I bought it, in an attempt to find where the various maps are hiding so I can actually dial the car in a bit better, but the reflashed image is definitely a significant improvement over stock; I tried a stock image with a few adjustments, where boost was quite a bit lower, and the car seemed to run significantly richer right across the board. So, until I can extract the fuel, timing, and boost maps from this aftermarket image, I'll leave it running that for now; it's significantly faster with the unknown maps. (One interesting change: the stationary rev limit was set to 6000 RPM, and a ton of timing appears to get pulled, resulting in very quick, very violent, building of boost at the line. Nice.)
Unfortunately, I'm basically starting from scratch with this image, like I did when I started tuning the 1g; I'm going to have to just block out large chunks of time to read the code and disassemblies other folks have done. (I don't even know what the registers are right now. ;-)
Overall, though, I'm extremely happy with the car so far. Planned changes to what I have right now include a downpipe/testpipe to finish off the exhaust, and probably a bit of playing with the stock boost control system to squeeze a few more PSI out of it (specifically, pulling a restrictor and resizing another one), although I'll need to get farther along with reading through this ROM before I'll be able to make significant boost changes without a manual boost controller. At that point, I think I'll be basically happy with the car; it's fast enough as-is.