Dunno if it's a bug, but I expected each of the direct upgrades to grant a size increase for a total of 4 stages (Base to Base+3). The first upgrade doesn't change size.
Palm slam also destroys "corpses", meaning they can't be claimed.
As for suggestions?
- When the invasion is done, allow the queen to suck up everything at once and let her grow to the appropriate size BEFORE hitting the victory screen.
- Palm Slam automatically absorbs anything it kills (Or it's another upgrade, also solves the "bug" above).
Aside from that, standard "expanded features" like upgrading towers, more Queen upgrades, more units, and maybe an infinite mode.