Just got a notice that Pidgin v2.4.1 was released. According to the changelog:
Treat AIM Unicode messages as UTF-16 rather than UCS-2; this should have no functional effect, other than continued support on systems which have dropped UCS-2 conversions.
As I noted, it was a major blocker for me to fully adopt Pidgin, but I guess they got the message from all the feedback they have been receiving. I just gave the new version a whirl, and it has indeed fixed AIM Unicode support.