Thanks for playing, and I really really appreciate the ideas! There's some good insight here and I actually did consider a few of them, or at least along similar lines.
Originally, my idea for the pixie collectors was that they also load the turrets, but I realized it was unecessarily convoluted for a jam. The turrets do use red so they do need ammunition but they just "magically" get it from you.
The shearer idea I do really like - splitting the task of extraction and collection. It would also give the collectors extra reason to transport red to turrets.
Using red as a building resource is really interesting, though splitting focus between building and defense was the main reason for having waves. But if the game were expanded to constructing more types of buildings that's definitely a good way to go about it