Thanks for everyone's tips, I've really made some more significant progress.
I feel kinda lame, because I really had no clue how much impact the power amp modeling would have... once I got the level and master working together properly with the power amp modeling enabled, the Plexi models *FINALLY* sounded like a real Plexi!. I didn't realize how much I was losing going into the return of my tube amp... I started playing old Free and Bad Company, ZZ Top and Aerosmith, bam, there were the tones. Tush sounded dead on...
I kinda think that maybe I wasn't into FRFR in the past because I wasn't giving it a fair shot at decent volume. Plus I'm not sure how much the Line6 claims of sounding more like a guitar amp are true, but that may also have alot to do with it.
With the volume up I'm really getting alot more guitar/amp interaction/interplay. So then I thought, let me pull up the Wreck Express, and mess around. I still have some tweaking on finding the right IR, but it's really responsive. Didn't seem to clean up as well as a real Wreck (well, at least the nice clone I had).
Next up: explore more of the non-master amps, like the Bassman, Hiwatt.
My wife just noted "You've been playing more guitar lately, why is that?". I guess if gear inspires you to play more, that's a good thing, right?