It all depends on how you ride it. I've had only one issue with the top gear bushing pop up, but I ride HARD and fast. On the other hand, my father (on an identical snowmobile) has never had an issue with his and it looks brand new (I guess that's what you get for going easy, whatever that is?). Neither of us have had any issues with the ROV, chain tensioner screw, driveshaft, or other common problem. Any warranty item that I've needed, Yamaha has stood behind at ZERO cost to me and has made sure to work with my shop to get me out on something so my weekends weren't wasted (something to keep in mind - BRP warranties have a deductible, Yamaha warranties do not).
HOWEVER, I did bend my tunnel last year when pulling my Sidewinder out of a enormous snowdrift at the shop. I can't blame that one on Yamaha - there were two guys on each side and one ON the tunnel. With a new tunnel riveted on this summer, I beefed that up with some reinforcement plates in a couple areas. Furthermore, most of my sled was torn down in order to install the new tunnel, including my chaincase. The dealership took a look at the top gear bushing (the second one) and it looks like it's in great condition with 4,000+ miles on it.
If you're going to leave well enough alone and ride a stock sled (no tunes), I'd suggest budgeting only a couple of items (sourced from Barn of Parts (BOP) - a local vendor to this site):
Barn of Parts (BOP)
1. Front Tunnel Saver ($35)
2. Center Shock Cross Shaft ($55)
3. Coolant Hose Saver ($85)
4. No Freeze Relay (2 relays x $20 = $40)
TOTAL: $215 - nothing that will "break the bank".
My Sidewinder (and the SR Viper that came before it) have been incredible machines that have allowed me to ride faster and harder through any trail condition compared to every legacy Yamaha that I've owned. Inevitably, that will come to bite me in the a**, but I can't complain as I'm putting the thing through tougher conditions (it's a "Catch 22" - it's all in how you ride it). Additionally, our Sidewinders are equals when looking at seasonal preventative maintenance when compared to the gamut of other Yamahas that we've had in our stable over the years. It's been nothing more than an oil change and some wax.