I'd love to see the rough cut of Star Trek III. I read the script, and there are many bits that didn't make it into the final film - such as Kirk consoling Bones as they're flying to Vulcan.
During the "Stealing the Enterprise" sequence, there is a section of music after McCoy's breakout that was scored, but not used - 20-30 seconds of footage, I think. A brief fight, I think.
I love Nimoy's direction in 3 and 4. One aspect I like about ST3 is the use of color. Lots of bright colors in the lighting - reds, pinks, greens, all very vivid. Nice contrast to the washed out look of TMP.