Team clutch (either one) would be a nice improvement. SLP porting, airbox kit, flo-rite air filters in the dash, handle bars riser and a bit of a gear down would make it a beast. SLP powder pro skiis are nice too. Then there is always the twin pipe setup from SLP.
The primary clutch, stock steering post, seat, trailing arms, xlite rear skid and hood are just fine. Porting the track is a waste of time. Fox shocks are nice if it currently has the ol nitrex shocks. Check the hifax. Install the ice scratchers. The skid plate is a good idea. The aftermarket belts are just fine. The nitrous is a waste of time. Rolled chain case is a waste of time. Avoid turning it into alphabet soup with 25 different parts from 25 different speed shops.
how old are you and what is your location?
great sled. Get yourself the Shop Manual and the Parts Manual and some basic clutch tools. With the books from Olav Aaen learn some basic priniciples of clutching and carbs and you are headed for serious fun. Keep her clean and greased and and in proper adjustment and that thing will run forever!