I can’t compare how much more awesome the newer kits are because I’ve only ridden mine, but here’s my take.
2013 ST kit. Fixed strut, wide ski, have not done the bearing upgrade yet. Has only about 20-25 full day rides on it. (Yeah I know.....)
Have had zero problems. None , nada, zilch. Have adjusted chain tension on both chains once and greased the skid and bearings a half dozen times. You could buy one of those for $2500 today and ride the snot out of it. It will be more about how beat up it is.
IMO, it’s just a snowmachine skid and a couple bearings. Not much to go wrong other than a couple wear parts or if a guy smashes it up. Any year model will be more about how much it was used and how well it was cared for.
There are a couple year specific issues, but they’re not big iirc. Bearings and chains.
What I would like is a LT or at least a 129.....I think. With deeper paddles compared to my kit.