Newer sleds ride better, but I don't know about $12,000+ better...that's up to you to decide.
I think a lot of folks that have new sleds probably have sat on an older model and thought "Wow, how the hell did I ever ride this?" which is exactly what I thought when I sat on my dad's '01 xc sp 800.
However, that sled hasn't been maintained for shit. Never had the shocks rebuilt, never replaced or cleaned clutch parts, I bet all he has done is replace hyfax, carbides, and put fuel and oil in it. It rides like a piece of shit.
Now in the next breath I jumped on the exact same sled (600 though) except that sled had the shocks rebuilt and had the skid gone through etc etc. Wayyyyy different, that one rode like a dream!
My girlfriend rides a '96 Indy Trail. The shocks had never been replaced, same story as the 800 above. Rode like shit. I put brand new gas shocks on it, a set of plastic skis off an Edge sled, lowered the gearing a notch and cleaned up the clutches as well as replace the clutch springs for her and it is so much better. Suits her needs, it reads that it goes 78 mph across a frozen lake.
It's silver because she climbed a tree with it the first time out. Didn't matter, she didn't get hurt, it was easy to fix, nobody had a loan on it and it was literally given to us for free.
People in our snowmobile club give us shit about it but guess who doesn't care. It rides the exact same trails they do at the exact same speeds they do (30-40 mph) and there isn't any payment to speak of and we have money to put towards other activities the other 9 months out of the year. She won't "use" the difference of $10,000+ for a brand new model sled. If something comes up that's a great deal we MIGHT hop on it but no rush. Not for the 6 times she rides out of the year during the possible 3 months of riding we might get. On top of that, guess what the insurance is on the thing...next to nothing.
I have a 2006 Fusion Dragon and have modded it to fit my needs. Bought it for under $3,000 3.5 years ago with less than 4,000 miles on it. Great sled, I'll probably ride it another 5.
http://www.hardcoresledder.com/forums/446-fusion/1662066-fusion-dragon-pics.html
Don't get me wrong, I like the new sleds and look forward to owning something like a Pro S 600 or XCR someday, but I'm not willing to bend over backwards and go into debt for it. It also depends on how you plan to use the sled and how it has been or will be maintained.
Hope that helps.