I've seen or have most of the mods out there for KISS Prem/LE, and the best KISS Prem/LE mod IMO is the Lovegun light mod. It lights up the back area when the ball levitates from the right ramp to that "Paul platform." Adds to the concert theme, really improving the game look in a measurable way, and is one of those mods that's so good it seems like it should have been there from the factory.
I got mine here (I haven't seen it for sale anywhere else):
http://www.kimballspinballs.com/kiss/