You can visit any Disney resort, and eat at any Disney restuarant no matter where you are staying. If you are traveling by car to see the resorts, at the guard gate, just mention that you are just wanting to look around at the resort. Some resorts give you a temporary parking permit and will direct you to guest parking. If you have a dining reservation at a particular resort, then you just tell them you are there for your meal and usually they have a pre-printed list of the dining reservation and will direct you where to park. Only place that may give you an issue with parking your car is Contemporary, or any of those along the monorail loop to MK ... Polynesian has been the easiest to park at. I guess some people try to park there and use Disney transportation to MK insteaf of parking at Ticket and Transportation Center. We have gone to the Contemporary to eat and they are sticklers about having a dining reservation, they have fewer parking places available now due to construction.
My MIL goes on the specific resort bus from different parks to walk around and check out the other resorts, especially this past holiday season. She was interested in looking at the resort decorations and did not have a car, so she bus hopped to see the resorts without a problem. They don;t make you show proof that you are staying at a particular resort to get on the transportation.