Would love to see this remade just slightly as an idleish game...
Make the enemies grow slowly stronger, based on the plants planted. (and enemies drop coins too)
Have the plants drop healing items when "harvested".
Add "collection" plants.
Have it so you can upgrade plants as well, or maybe "hybridize" them, by sacrificing two seeds to create a seed that has the abilities/attributes of the other two?
Use a day/night cycle, where plants are only active during the night, and are normal plants during the day?
Resident evil meets farming sim?