Interesting idea, but it was really just an exercise in metagaming - beat up rocks, collect money, buy upgrades; lather, rinse, repeat. And once you realize that you get more points for doing more damage, it becomes obvious what you have to do: invest all you can into power upgrades until you can max out everything else in a breeze.
The downside to all this is that the game is very quickly not about typing correctly anymore; when "killing" the rock only takes a few "rounds", you don't need much skill, and with your combo timer upgrades, you don't need to be fast to get combos, either. Speaking of combos, BTW: being able to beat the rock very quickly also meant that the "max combo" stat became useless; it simply wasn't possible to attain high combos anymore, as the rock'd shatter first.
Concerning power updates, is there a limit to them, BTW? I went up to a power of 125000 without hitting one. Also, a minor glitch: once your power goes beyond 100k, the full number may not show anymore, depending on what it is exactly: there isn't enough room for it.
Outside of this, there were a few minor problems I'd suggest fixing; the power section of the shop also said "Time Section" at the top, and there was no way to directly play again without visiting the shop first.
Oh, and amusingly, once I was able to beat the rock with just six keypresses (no space!), I wasn't able to collect the bonus points awarded at the end of a "round" anymore. As a result, I was never able to attain a score other than 750,000 anymore.