A key problem in the design of No Pain No Grain is that the player can make the game very boring and easy for themselves. This is not too much of a problem in the early game as things are supposed to be easy. We just want to not drag it out too long; let people get to the interesting stuff rapidly. However I'm not fully sure of what shape this interesting stuff will take.
So how it works right now is that you chuck seeds into the ground, as many as you want and whatever type you want, and you can usually circlestrafe their attacks and remain completely save. In the case of moneystalks they all literally shoot in the same direction. This is a problem because if someone plants any number of moneystalks they will encounter zero challenge, at least until the radius of the blob of plants becomes so huge that they can't walk out of the way of the unfathomable wall of bullets in time. Okay, you might say, just make them shoot in different directions, or in different ways that circlestrafing would not render trivial. This is one possible solution; a few plants already employ it like asparaguns and red hot pokers. Plants that lead their shots, shoot in many directions, spread out their shots or move... there are a lot of potential patterns that could solve the problem of triviality and banality. But this leaves behind a lesser problem: You'll just have a bunch of plants of the same type doing the exact same thing at any given time. Ten nukumbers or twenty gunflowers or fifty moneystalks. Perhaps it is wise to come up with some incentive to plant multiple different types of plants. This I hint at in the intro video - plants that auto-water nearby plants but also attack themselves could spice things up. Plants that make others drop more loot but also beef up their projectiles. There are a thousand slight carrots I can offer in exchange for the mild inconvenience of planting multiple species at the same time and I think I'll enjoy trying some of them out.