by benuk01 » Tue Sep 20, 2011 9:21 am
This caught me out the first few times I played Kingdom Rush. I thought "I'm not paying 350 for a single death ray shot!" and kept my money for other upgrades. Oops!
As far as I can remember, all the upgrades in Kingdom Rush activate a permanent extra power for the tower in question, including the stone elemental power (re-spawns shortly after death). As Quest and Julian point out, further upgrades improve (amongst other things) the cooldown time for these special powers.
The only (sort of) exception to this rule is when there is a special feature on the level like the Sylvan Elves or Sasquatch. You're paying your money for individual units, not to activate a feature that will re-spawn the unit after a certain amount of time.
Ben