The only differences I've actually noticed so far are the new lights, the fighter beams, Alt-Pause, and the headlights.
I mean, what's the point of increasing the engine's power to put in more pixels per scene? The people with new hardware can now crush Freespace, bench-mark-wise, and the ppl with older hardware don't have the power required for it (most likely, T&L, arguably the most benneficial thing that's being added, won't be supported by those low-end ppl's video cards).
It might add about 20 FPS, but with a game that any PC bought within the past 3 to 4 years can run without difficulty, it's not like without that incrememntal boost, it's going to rock our world.
Just my $0.02
Don't get me wrong, I think the SCP is a great effort by the community, but the things that are immediately noticable should be put in first, along with anything required to run it, then the background stuff. Also, we're putting in new abilities for texturing, right? Well, what's the point of doing that if you're still using 4 to 5 year-old textures? The SCP should be expanded to also have an update for the stuff already in the game.