Greta,
I used to use the "threads not read" thing, too.....till I discovered an easier way. Well, easier for me.
When I first sign in, still at the home page of this forum, in the gray box on the right I click on the link that takes me to messages I've particiapted in. (especially if I'm short on time. Easy to follow up on threads/mssgs) Then, after I've read those, I go up to the top banner to click on "Forums." It's really easy to see what threads have new mssgs because those will be bolded. Under NCRA, for example, there's three choices - Information and issues, NCRA Online, and test area. If any of them are bolded, I'll click. That'll bring you to a page that shows all the threads in that section. Again, the ones with new mssgs are in bold.
There's no way (far as I know) to know how many mssgs are new, but I find it's easier for me to track what's going on. Oh, you'll be able to see how many mssgs are in the whole thread, just not how many are new mssgs. One you click on the thread you'll still have to scroll around till you find where you left off last - not the most efficient, IMHO. I'd like an easier way to know where I left off last, especially when it's a really active thread.
So not sure that'll help or whether that will be to your liking, but might be worth trying (if you haven't already).