Alright, Jimm! Thanks for your help!
"The implicit assumption is that authors only change the description, etc when adding new chapters or the 'last updated' date will be updated when they do so."
Seems perfectly reasonable to me.
"Sounds like you want 'Update Always'. That will always update the metadata both in calibre and the epub titlepage, but only download chapters if there are new chapters."
Oooh, that sounds good. I didn't even think to use "Update Always". Looks like it does exactly what I'm hoping. Awesome! I appreciate the reply.