Compression numbers vary a lot depending on elevation... I'm at 7k' and my 5500 mile '09 is showing just over 90psi. If I was at sea level,I would probably get closer to 110. For an '09, I don't think that's too low.
The '10's were slightly higher compression motors, so you should see a bit higher compression numbers, better than 120 at sea level would be ideal.
It is honestly more important that the two cylinders are fairly close than to go looking for an actual number, since I've seen different correction factors for elevation. Different gages give different values too. FWIW, don't use a HF compression tester, it'll give you WAY low numbers on small engines...
I'm not sure there's a more bulletproof engine than the cat 800 that was in these sleds. No reason you shouldn't get 5000 miles out of it before a top end, so long as you don't frequently overheat it or run it out of oil...
As for maintenance, pull the cover off the DD and make sure it has the wide bearing. If it doesn't, put one in. Fresh DD fluid every year doesn't hurt. I run synthetic 80W140. I used to cut it just a little with ATF, but haven't bothered at the last two changes.
Disconnect the power valve cables from the servo and pull and release each one. They should pull smoothly, and release with a clunk. If they're sticky clean the powervalves. I have never cleaned mine, and they're fine. Prior to this year I ONLY ran APV oil.
Check the Y-pipe for cracks. Check the engine mounts and replace them if they look torn or heavily distorted.
Check the bulkhead for cracking behind the engine, just in front of where the steering shaft hits it. Several fixes available.
If it doesn't have the guards for the kill and warmer switches, buy them. Best $20 you can spend... I put an SLP can on mine, but just went back to the stock can this year. I didn't see any perf gain, only more noise. Weight difference wasn't worth talking about. I'd leave it stock and just go ride.
Biggest bang for the buck if you ride steep and deep would be a 2.5" CE or 2.6" PC track. I'm about to do that to my turbo sled, since it's running a Maverick track that pretty much sucks. My other sled has a 2.25" PC and it's pretty good. The 2.6" is even better though.
And let me know if you want to trade a '09 style seat for the '10 seat... My HCR has the taller '10/11 "Mountain" seat, and I'd love to get one for my Sno Pro.