On my own behalf:
I got my first ever rating for my games on Itch.IO and I look like the cat that got the cream. :-)
Feedback is extremely important for me to see how I can make my next game better.
In the rating, the player says he would like speed increases on certain numbers of upgrades.
In case anyone else is wondering:
I deliberately didn't program it because the PP makes it possible to completely adapt the game to your own needs. (income, speed and price)
Hope you still enjoy it.