If yours came with one of those stick antennas, replace it with a cloverleaf one. That should be upgrade #1.
Then maybe look into running the entire thing off its own battery vs tapping into the lipo pack.
As far as detail.....you're pretty much going to be limited by the camera and not the display. Not sure what the resolution of your camera is, but the one that came with the fatshark kit is kind of meh as far as detail goes. Sony I think makes a really nice one. Look around on youtube and look up comparison videos by some reputable people. RCModelReviews is one guy that's based in New Zealand, and he really knows his stuff.
https://www.youtube.com/user/RCModelReviews