I did some more research today and discovered some Apple docs that helped. I now have it fully resolved and up & functioning again. I did lose the changes I'd made in my iPhone's calendar, since mid-week, as it defaulted back to my iMac's iCal. But it's only a few days of changes, so better that I lost that and have it working again, than not be able to sync on a daily basis.
Here's what I found via iCal Help: "Sync Services: Advanced troubleshooting for contact and calendar syncing".
I followed those instructions, and once I'd reset sync history, all I had to do was resolve the outstanding 1140 conflicts. It started with 840, which I resolved easily & quickly by selecting the checkbox that applied the same resolution to similar conflicts. Then I had a few I had to handle indiviually. Then the remainder of the 1140 showed up and I treated them like the first 840.
Hope this resolution helps someone else, too. It took me awhile to find.
Well ... the problem started again today!
So I had 3 days when my calendar stopped syncing -- those were very bad days, as a result! Then it synced when I followed the above procedure.
Now that I'm back to work from the weekend, the problem is back!
What has caused this problem to to start? Is there a bug with the latest iOS? Or is it a bug with the latest iTunes? Maybe I should not have upgraded either until I'd heard about the fall-out!
Either way, I'm now in trouble -- if my calendars don't sync, it is a big problem for me!