Thanks much for the reply!  You've given me quite the list for further research.  I'm looking forward to it.

I have since discovered a side effect of the html email alerts in that our SEPM's httpd.exe was acting wonky, taking lots of processor and not letting go mostly.  Investigating this, I "discovered" the tomcat\temp folder which held over 81000 .png files going back almost exactly one year.  Considering the average New Risk Alert email contains nine little pie charts, it's not that surprising to find the system was generating over 200 of these little graphics a day.  I cleaned out all but the last ten days worth, leaving only 2273 files in this temp directory.

Can't say yet that there's any direct causal link between the number of temp files and httpd's occasional acting out, but it occur to me that if SEPM were generating plain text alerts, there'd have been no need for thousands of little graphics files nor .mht files.