Thanks for the info tipanii. Looks like I found a bug with the game. Maybe that is why I am finding it so hard to get any further in the game. I keep doing levels over and over again.
Yes it seems you can only upgrade past level 3 if you equip a star badge. The guide for the game has videos that show all towers being upgraded to level 5. Either they have changed the game or they were cheating in those videos. This can confuse people because they see and know towers can be upgraded past level 3 yet there is no information anywhere that explains how to do so. Eventually you find out that it can only be done with a star badge even though the videos show that you can upgrade any gomphus past level 3 with or without the star badge.
So the guide (walkthroughs) for the game are somewhat pointless because they use a strategy that you are unable to use. Good game though.
Clicking upgrade doesn't work. It shows an upgrade cost of 100 and clicking on it doesn't do anything. Only twice has it shown a cost of 800+ and actually allowed to upgrade above level 3.
I did it! The Immaculate Desk Badge (impossible – 60 points) Some of these are really tough. Great game! I would like to see 2.0 with these graphics but the options from 1.9.
Bunny Invasion 2 has the most foul, cruel, and bad-tempered rodents you ever set eyes on! These rabbit's got a vicious streak a mile wide! They're killers!
 "Rings"){kind=icon}
 "Rage 3"){kind=icon}
 "Interactive Buddy"){kind=icon}
 "Mushroom Revolution"){kind=icon}
 "Bloody Fun Day"){kind=icon}
 "Desktop Tower Defense 1.5"){kind=icon}
 "Bunny Invasion 2"){kind=icon}
 "Bubble Tanks 2"){kind=icon}
 "Sonny"){kind=icon}
 "Fancy Pants Adventure: World 2"){kind=icon}
 "Scriball"){kind=icon}
 "Super Energy Apocalypse : RECYCLED!"){kind=icon}
 "Perfect Balance"){kind=icon}