A few thoughts:
1) I can't speak to the post-ROL crowds and the effect on FoP, but generally the wait at the end of the evening has been reported as pretty good. RD may get you on the ride faster once you're in Pandora - but you'll spend some time waiting at the gates and on the bridge before you get in.
2) I won't say that they haven't opened the FP queue at RD to move the first standby people through, but I've done RD a couple of times and never saw that. The chain stayed up on the FP line until 9 am and everyone at RD was lined up in the standby queue. Even if they did, there are so many people at RD that they couldn't keep the FP side open long without backing it up towards Africa.
3) Now for the main question - I wouldn't worry about missing anything in the standby queue (and you don't miss any pre-show). Most of what you'll miss is the concrete path leading from Pandora to Africa where you'll stand for much of the wait. The best part of the standby line is the outside part that winds under the floating mountains and past the waterfalls - beautiful work they did there and it does "prepare" you for the ride. Inside, you'll have less time in the cave (not terribly interesting - some cave paintings and artifacts hanging from the rock), you'll be a row removed from the window to the lab (if you like pressing your face up against glass trying to see into a dark mostly featureless room then this might be disappointing), and then the FP/standby merge occurs and you're in the sterile concrete "bunker". In all honesty, I was far less impressed with the queue than I thought I'd be after reading previews. It's well done but not essential. As for the preshows? There are none in the queue. But you'll get two once you start the ride. Prepare to get to know Dr. Stephens very well. You'll wish you could skip him a few minutes into all his tests.
