Thank you for playing and for your feedback !
For the upgrades, right now the player gets them every 30 seconds.
We didn't went more deeply into this mechanic, and now that you point it out, yes I think some sort of visual feedback would nice.
Also switching the timer mechanic to an xp system, seems like a way to go.
Xp could give a bit of RPG feels, that could fit the game really well !