Update 2 to “In search of a wireless router that doesn’t suck”:
I got a lot more strong recommendations for the Apple Airport Extreme from many tech experts, including Ars Technica’s David Chartier. It was tempting, but there are just too many people reporting the same crash/require-reset problems that plague the $40 routers. If it were anywhere near that price, I might be willing to take the risk — but not for $180, a price approaching the far-more-reliable options.
After considering everyone’s (excellent) feedback on this and weighing a few decent options, I’ve decided to go with this embedded system with pfSense. (I learned that m0n0wall doesn’t support UPnP.) I may regret the complexity of the initial configuration process — I’m hoping that it comes with reasonable defaults and I won’t actually ever need to connect a null-modem cable — but after the basic setup, it looks like everything’s available in the (very nice looking) web GUI. This probably isn’t an option that non-geeks should ever consider, unfortunately. (But I really doubt that any non-geeks are still reading by this point.)
In a week or two, once I’ve had time to set it up and use it for a while, I’ll update again with my experiences so far.