We ended up in both types of rooms last August (due to a leaky pipe). We had paid for GV, so the upgrades were nice.
From our lagoon view in Big Pine Key, we could see the Polynesian and wedding pavillion. It was very nice.
From our theme park view room in Boca Chica, we could hear the music from Main Street and the train whistles. We could also see the castle and BLT over to the side. We also saw the fireworks. I don't remember about the water pageant.
I'm not one to splurge on views because we do not spend a lot of time on our balcony, but both views were nice, especially for us since we did not pay extra for them.
I'm not sure what's worth it to you. Certainly, seeing the MK was magical. The lagoon view room was very nice but not as special as that MK view.