Assuming weather is cyclical and there will be enough snow most years to keep it interesting, I think snowmobiling will be ok because:
1. Multi-use trail system - should help to maintain the infrastructure, for the most part. Of course the trail network will always be fragile, and new land to ride will never be created, so it's not guaranteed.
2. Used sleds can be purchased at decent prices that probably will be better to ride than a new sled from years ago. Just my opinion. The high end sleds are getting ridiculously expensive, but if you compare apples to apples, what you can get off the used market with say a 600 carb is pretty good for the money. Plus resale has been good.
3. If you want to ride high miles, you have to pick a sled that is easy on gas - a used Yami or one of the skidoo DI's for example. They (Yamis) might not be the best handling sled, but better than anything 20 years ago. Again, just my opinion. Something I've tried to do when planning a day's trip is to eliminate riding on RR grades as much as possible. They really aren't fun, and they basically just burn money to get from point a to b.
4. International sales are growing - overseas sales were greater than US or Canada sales this past year for the first time ever. This trend should help control costs.
5. If renting, heading out West is not a bad deal at all. You can do that for $200/day. You can't do that in the UP, once you add in gas and oil costs.
Gas prices are the biggest concern I have. That is why I haven't gone riding in Canada in about 10 years. How many people would ride up there if snowmobiling gas was the same price as here? Also, as Moose mentioned, the cost of moving the sleds around to go on a trip is getting insane. That's what I've been trying to figure out how to control the best.