Hopefully my final post here. I think I've fixed everything.
In Outlook 2007, I went to View...Events... and was able to see all the Holidays previously imported, which are basically messed up on my TP2. I selected and deleted all of these. Again, I did this with my TP2 connected via ActiveSync. It took a minute or so to Sync, and all Holidays were removed from my TP2.
I then went in Outlook 2007 to Tools...Options...Calendar Options...Add Holidays... and again imported U.S. Holidays. It warned me that these had been previously imported, but allowed me to do it again. Once again, it took a minute or so to Sync with my TP2, and now these Holidays seem to be present on the correct days.
So after hours devoted to this problem, I'm back to where I should have been to begin with, having a Calendar that actually shows the correct dates and times for events!!
The only thing that is different is that I haven't re-enabled Network Time Sync. While I don't see why that should make a difference, I'm also reluctant to upset the status quo. Perhaps I'll do an SPB backup first, and then try that out.
Hope this will be of help to others with these problems.