Thanks a lot for the feedback. You're not the first person to point out the speed up should be toggle and after the rating period that's definitely one thing I'm going to change.
The balancing was definitely the hardest part for me even with my friends playtesting. I think it's also a matter of with how limited tower spots are so there's just no benefit to placing towers other than spears and furnaces.
Scaling I feel like has mostly to do with how easy the interest mechanic makes the game if you use it correctly. A potential fix I've been thinking of would possibly be to nerf the max. interest, but I'm not sure.
Anyway, thanks for playing my game and I'm really flattered by your kind words!