I really didn't intend to continue fixing this low-quality photo, but it does make for a good test of skills. I used some of the selection techniques I've been seeing in Helen's other videos to select the foreground hills and trees, then made an adjustment layer (curves) and -- lo and behold -- it worked as I hoped! With just that portion selected, I adjusted the curves to get more color and light in the hills. Then I used the brush to paint on the layer mask to help the trees in the middle right third. These trees are too sparse to include in the adjustment layer because it lightened the background behind them and looked awful. I changed the selection to the darkest "hill line" behind those trees, did the adjustments, then went back with a really soft brush and just blended and highlighted the sparse trees a tiny bit.
The photobombing goose project has inspired me -- I really might have to keep going now and get rid of the foreground post and the dirt road next. :)