Right now the bike path up Vail Pass is blocked by snow. A co-worker tried to ride west from Frisco and got stopped by snow a few miles short of Copper Mountain. The snow is melting fast, though, so call a bike shop in Summit County the day of your ride and get a condition report. It is a spectacular ride, though. The bike path does go between the east and westbound lanes of I-70 from copper mountain to the top of Vail Pass. The two halves of the Interstate are on opposite sides of the canyon, well above the level of the bike path, so you really can't tell that you're on the center strip of an Interstate Highway.
The loop around Lake Dillon involves around 800-900 feet of climbing, most of it on Swan Mountain road. The ride is mostly on bike paths, but part of the ride is on Swan Mountain Road, which is narrow, winding and mostly shoulderless. It's well known as a bike route and drivers around here are fairly courteous to cyclists, but it's not a bike path and anyone riding it should be comfortable riding in traffic on a narrow road with no shoulder.
Here's some more info about cycling in Summit county:
http://summitdailynews.co.ussrv15.ne...?date=20100513