I didn't get into the pros and cons on purpose because they have yet to be discussed, so getting into that at this point would turn it into an opinion piece, which I wanted to avoid.
Purely in my opinion:
Pros:
1. Move traffic out of sight
2. Environmentally more friendly
3. "weatherproof"
4. Allows quick access between resorts
Cons:
1. Need to dispose of tailings
2. Expensive
3. Allows more traffic into canyons (would happen anyway?)
That's just a quick list off the top of my head -- I'm sure that there are many, many others.