I don't know about a multiple machine summary, similar to Nagios/Spiceworks.
I just do like you do. I keep HWINFO and the summaries open and check on them once in awhile.
I suppose you could have HWINFO or GPU-Z to save a logfile in a dropbox and check on that instead.
Ah, I believe someone had a proxy website they built to automatically fail-over pools and check on mining stats.
The proxy might be a little overkill for just monitoring, but it is a possibility. What I'm looking for is a overview of all my nodes with rates, temperatures, etc (see: https://i.imgur.com/kEc5O.jpg for an example)