So, I bought Into the Future. Then I built a PlumBot gardener and added solar powered and efficient. (Of course.) Next, I unleashed him on my money trees. The result? Almost fully automated care of the trees. All I had to do was instruct him to plant newly dropped seeds, optimum fertilize (which only seems to need to be done once per tree thus far), and periodically sell the money bags.
One perfect tree is easily $1.5-2k a harvest. Keep adding trees and the number just keeps going up. Of course, when the grove gets large enough, you'll need another gardener. Still, nothing is perfect.
Meanwhile, you're living large and doing whatever you want thanks to a constant, renewable source of income.
Which makes me wonder - has anyone found an easier way?