Something I've noticed: If you get killed instead of beating the level, it feels like you get more gold. So I've just been standing ground and shooting things until I die. Much faster than actually beating levels.
Why aren't frags free on this? On Mochigames, they are...
Btw, love the addition of Dartling Gun and Spike Towers. I haven't played this game in a while, and am glad to have returned.