I love visiting other resorts. I don't have a car as I fly, and find Disney transportation to be easy.
On a day you are visiting Epcot:
Walk out the IG (back entry between France and England) to check out the BC, YC and BW lobbies. ESPN club is there, Beaches and Cream, Cape May Buffet, etc. when I'm done browsing around I take the boat on over to DHS just because I like boat rides.
On a day you are visiting MK:
Take a break from the park and grab the resort monorail and check out each of the resorts. I especially like the Basin White store in the GF and just listening to the grand piano player in the lobby. Grabbing a bite to eat and sitting outside at the CS at the GF or the Poly is fun too. Note you can walk from/to the TTC and Poly. You can also take a boat to/from each of these resorts and MK. Another option is to boat from the front of MK to the Wilderness lodge and check out it's grand lobby or over to Fort Wilderness.
On a day you are visiting AK:
Head on over to the AKL. The gift shop is great. The lobby is beautiful. You can wander out to Arusha overlook and check out the animals on the savanna. This is one I'd consider driving to if I was visiting after AK park was closing, as they close early.
I suspect Disney's theory is if you visit their resorts you'll fall in love with one and next visit you'll stay on site