The Westin in Avon (Beaver Creek) is one of my favorite hotels anywhere, any brand, Marriott or not. We tend to go in the summer (it's gorgeous up there) so I can't speak to relative value vs. other options during peak ski season. It's just one of our happy places in this world when the town and resort aren't that crowded.

If you want to ski for Cat 4, I can't think of any real on-the-mountain options unless maybe Marriott is doing something ski-related in Korea or China. I have known people who've based a ski trip in Salt Lake City so they could ski different mountains, but they had to drive every day to do it. If it's a Travel Package certificate, you can always phone to upgrade it. If it's a credit card certificate, you can't.