Brian,
The way I see it, the most economical way to get everything (and not double up moving forward) is to take the plunge for the Ultrapak one time. You may double up on some tracks this one time, but it is a one time plunge, and if updates/improvements have been made to your existing RealTracks you get those updates.
After you do this once the Pluspak simply gets you the new RTs and the new program (no more doubling up) moving forward.

This is why longtime users often suggest getting as much as you can right away.
If you can swing the Ultrapak once you'll never wonder if you have everything and get the complete updates & new RTs for the best price every year moving forward.

For first timer buyers that looks like $569, but if I were you I'd call them (or chat) and see if the 2018 upgrade/crossgrade option for $199 would be allowed for you since you have purchased a 2018 version previously.
Since you've bought once already I'm guessing you'll be good. Call it a hunch.
Can't hurt to try, and no harm no foul.

If so, you could get that and just go with Pluspak moving forward, save in the long run for the year-after-year updates and know you have everything every year.

Once you do this, all RTs are available as downloads in your PGMusic account, along with the current version.
I did find a spot to check your upgrade costs from a previous version
https://www.pgmusic.com/bbwin.packages.htm
Scroll down a bit

Personally I'd just call and ask though .. or chat

Make your sound your own!
.. I do not work here, but the benefits are still awesome