I honestly think it depends on how much time you are going to actually spend in the room. Having all the amenities is nice if you like to take breaks from the park and hang out in your room a while, watch tv, take naps. A microwave is only necessary if you are going to use it. If it's just a place to sleep, shower, eat breakfast, then maybe you don't really need a Premium.
We had been going to stay there in the Premium rooms for this next trip, but we decided to go ahead and stay onsite. We wanted the premium rooms since they are bigger and have all the amenities, and we planned on spending some actual time in the room to take breaks and stuff since we will be there for 5 days. And the option of having breakfast brought to our room in the mornings was a great thing as well.