Please let me know if there is anything I can do to help make this more useful.
What can I say? Rebuid your bitcoind without stripping the debug symbols. The default makefile.unix already has "-g" to enable debugging.
Sounds good! I will recompile bitcoind with debug symbols included, and try to get a better backtrace.
In the meantime, I will continue to leave things running with a longer wallet unlock timeout for the next few days, or until another crash occurs, since that does seem to be a promising lead.
Thanks again for the help!