Hyannis/West Yarmouth is definately a tourist trap area.. About all I'd do there is minature golf..
If you like bike riding I'd go to Brewster, MA (mid cape) and ride the bike trail all along the national seashore hitting the world famous Nauset beach, Chatham and places like that..
Martha's Vineyard is also a very nice place to ride a bike.. plan a day trip there, take the ferry down from Woods Hole..
Do you like fishing? Deep sea fishing expeditions leave from Hyannis daily..
Heck, the Cape is not that far from Boston (about 1.5 hours) plan a day to go up to Boston and sightseeing around there..
As someone else mentioned, Newport RI is also not very far away.. and is also a gorgeous.. the Cliff walk is awsome as is window shopping on Thames Street, ft Adams and the very old mansions in Newport are open for tours.