OK, my thoughts: I would draw a big X through Lake Powell. It's really not that interesting or pleasant. It's going to be MUCH too hot to enjoy the lake, which by the way is heavily polluted, especially with recent low water levels. And it is often very windy at Wahweap. 109 degrees and blowing dust doth not a pleasant experience make.
As you're coming from the west, going to Estes Park and then into Rocky Mountain NP is a bit of a double-back. Suggest you enter the park from the west via Grand Lake. Beautiful drive!
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Ditto on both of those. Lake Powell and the dam are drive thrus with maybe an hour or so touring the dam