Originally Posted by
PrincessCupOButter
Unfortunately no. The harvest boost does not double the amount of coins dropped during harvesting. Several players tested that out during the first set of mermaid goals. However, it does double the amount of whaterever is being harvested, plus any special drops. (So if a dark plant drops while harvesting felloras, those will be doubled, which is helpful for those working on 'sister, sister') I believe I read a post earlier that the dark pollen drops were doubled (I'm not there yet....still trying to get enough storm water to craft the necklace. :( ) And any energy return is also doubled while the boost is active. So it's still a pretty helpful little boost.
For high coin drops, don't forget the little fairy houses, fairy bulbs, the cathedral, and the forgotten roost. They all drop 2k+ coins. Well worth the energy imo.