I discovered that the problem with g++ 4.3 segfaulting on spinmc_factory has been logged with GCC Bugzilla - http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38369 - and that the problem persists in 4.3.3, which I discovered on my own prior to finding that bug report.
According to the bug report, GCC 4.4.0 corrects whatever the problem is, so ALPS spinmc users reliant upon GCC might want to skip from GCC 4.2 to 4.4 (whenever it appears) or resign themselves to the poor performance of "-O0" with 4.3 as reported previously.
Jeff