FYI-at Plaza Inn we always get our cups to go. The cashiers have them, you just have to ask. That way we can get a refill before we leave to take into the park. But no, I'm not condoning using the cup for refills all day. I thought of this myself years ago but we don't do it. However, I am sure there are those guests who do.
When we get refills at Pizza Port I've never had anyone ask to see our receipt. I never heard of the "one refill" rule. Not saying they don't have it, just haven't run across it.If you are still eating and wanted a 2nd refill I don't think it would be a problem.
Since we are APH and go quite often, we don't buy that many sodas to start with. I'll bring in my own Diet Coke, we'll get free cups of water (hot or cold), and DD loves those flavor tubes for water. When I do buy a soda it is usually at a place where I can get a refill. If I can only get one serving, that's too much $$ for me.
Oh, and one more that allows refills is at GC. One of our fav. CS, Whitewater Snacks.