Just wanted to follow up on this, as we are just back home from Amanpulo - a trip report will follow. We ended up staying the first four of our eight nights in Casita 40. There was a lot to like about it - the view was great, and the villas weren't as big a problem with the view as they seem to be in some of the pictures. The trees have grown up around them (sorry, I meant to take pictures but totally forgot), so they were not as obtrusive visually as I expected. We enjoyed sitting on the terrace, especially in the early evening when we were visited by the huge yet fascinating fruit bats that live up in the hilltops. We did end up moving to Beach Casita #1 for the last four nights, partly for a change of pace, but mostly because Villa 7 (which had been empty for the first half of our stay) was then occupied by a fairly raucous group - loud music, hooting, etc. and Casita 40 and Villa 7 are just too close together, IMO. Resort management intervened to mitigate the noise somewhat, but we decided to try a different Casita, and also enjoyed being down on the beach very much for the last half of our stay. The other big takeaway we would share is that we found the beach to be much cleaner on the west side of the island. I don't know whether that was because that's just where the current tended to bring debris (my guess) or whether the resort was just more attentive to cleanliness on the west side than the east, but we noticed a considerable difference between one and the other.

Will post a proper trip report when time permits.