@unstabl_mind: An interesting idea, but probably won't be implemented simply due to the possibility of losing MOST OR ALL of your angels. Imagine if you lost a whole bunch of angels right after restarting and buying a big angel costing upgrade.
Ok, I figured out how continuing in Infinite Mode works. If you die, you can select one of the other characters you've unlocked (they'll have a blue rectangle around them) and continue playing with them. If you DON'T want to continue, press left or right until you aren't highlighting any of them and then press Space. I hope this helps people.
@thundernova308: Well, when you fly in a plane and look out the window at the ground from high up, everything DOES look pretty bland. It's only when you get close to the ground and can distinguish between different objects and see the flowers that things begin to look pretty.
@FaustTheSad: For what Faust DIDN'T say, is that you can keep Wave 1 alive for each battle until the very end, allowing you to not have to fight the later harder waves in each stage.
@keitho2314: While viewing your city, click the Setting button near the upper-right part of the game screen, and then you can turn the sound setting off by repeatedly clicking the minus sign.
@meurz: You can complete 2 challenges per level, so by Lv. 40 you can complete 80 challenges. Since you only need to complete 70 for the Hard Badge, you can get the Hard Badge before you get the Medium Badge.
 "AdVenture Capitalist"){kind=icon}
 "Orbital Onslaught"){kind=icon}
 "Deeper Sleep"){kind=icon}
 "Liquid Measure 2"){kind=icon}
 "NoNoSparks: The Ark"){kind=icon}
 "High Tea"){kind=icon}
 "Run 3"){kind=icon}
 "SteamBirds"){kind=icon}
 "The Great Siege"){kind=icon}
 "Roadkill Revenge"){kind=icon}
 "Building Rush"){kind=icon}
You can also click outside the window if you don't want to continue.