Lighter??? I seem to have done nothing but add weight to mine since I got it! Muff pot, powder pro skis, and Evol X front shocks to name a few things. All worthwhile trades for me though. Mine is getting a belt drive next season for sure. Might put on a Diamond S quiet can and chromoly lower a-arms if I have a little extra in the sled fund next fall. After that I think I'll leave it alone and focus on cutting more weight off of the rider. I'm with mmsports, the durability seems to be pretty good for me on my pro-lite as it sits other than my latest bent rail incident (can't fault the sled too bad for that one).
If I was on a light weight mission without a budget, this is what I would do above what my pro-lite currently has on it:
Belt drive
Carbon Tunnel
Carbon Tank
Carbon rails
Carbon body work
Carbon or Ti handlebar
Carbon clutch outer cover with Ti bolts
Ti exhaust can
Ti a-arms and skid arms
Ti steering post in the "standard" laydown configuration
Ti engine and chassis bolts
Stock or polaris gripper skis
Stock float ski and rear arm shocks
Float front arm shock
Tiny stock front bumper
Ditch all lights entirely
Install a Polaris 800 motor (yeah right)