Here's what we did (we were also staying at POR). After day 1 at MK (being up from 7am-11pm+) and day 2 at Epcot (being up from 7am-midnight), we were exhausted, so we took a day off from the parks. (We had planned to take this as a day off from the parks, but I had underestimated just how tiring it would be touring the parkswhen we were there, MKs hours were 9a-9p and Epcots were 9a-10pand were criss-crossed the parks several times). So, on day 3, we slept in a bit, went to PO-FQ to spend some time at that theme pool, then went back to PO-R and spent some time at Ol Man Island pool and playground. Then we caught the Disney bus to MK (didn't go to the park, just took that bus to get over to the boats that take you to the Deluxe resorts). We rode the boat over to the Polynesian. We looked around there a little, saw the pool, etc, then boarded the monorail and rode the resort loop. We didn't get off at the other resorts, although we might next time, just to look around. We got off the resort monorail at the TTC and rode the other monorail (from that loop you can see it a lot of Epcot). When we got off that monorail, we took the boat over to the Yacht and Beach Club, looked around there (quite an impressive pool) and ate burgers at Beaches and Cream. Then we took the first boat that came that was going to a location where we could pick up a bus to POR (I think we headed for MGM if I remember right) and took the bus back to POR.
I had also considered going back to the Poly to watch the Electrical Water Pageant, but since we were getting up early the next day, we decided to return to POR and rest up instead. Another option after the Y&B club would have been to take Disney Transportation (I think a boat would have done it) to Downtown Disney, spend some time there, and then take the boat directly from DD back to POR.
It was a slower paced day, and we enjoyed it. I would not want to spend time riding the monorail on the same day that I was using a pass at the parks. I feel like if I'm paying for park admission, I want to take advantage of all the parks have to offer on that day and I don't want to spend time on activities that I can do for free on another day.