Board Thread:Bloons Wiki and BTD News/@comment-3153244-20130925070022/@comment-3153244-20131120111525

They keep their upgrades, yes, but for that tower.

So if you for some reason decided to switch back to a Sniper Monkey, you would have your 0-2 upgrades. You can always go back to the resting area as Nick and Dani are doing right now to farm for your new towers' upgrades.

If a player's upgrades for one tower carry over to another tower, this can be abused, in terms of the energy prerequisite. Energy Prerequisite is a reflection of that upgrade's power.

If a player upgrades their Dart Monkey to 0/2 (EP: 0/1 - 11, 0/2 - 14), and switches to a Boomerang Thrower, how do you think someone who has spent many turns of effort getting their Boomerang to 0/2 (EP: 0/1 - 13, 0/2 - 16) would feel?