I think that you should be able to upgrade the weapons with money as well. I feel like there was too much time between buying new items, which caused a lot of "grinding" at some points.
Here, I can tell you how to easily solve ANY of Dim's levels. Throw a detonation bomb at the backdrop. The bomb will roll down past the people. Blow it up by the person closest to the ground. Rinse and repeat. There, that's half the game done!
*New Dim level comes up*
Me: Tries to get gold by using precision and luck....
-Selects the group of three bombs-
"WAHAHAHA TAKE THIS DIM"
-Finishes on shot 17-
During my battle with the Colossal Guardian it glitched and he ran literally into the wall. Then he couldn't hit me and I couldn't hit him. I had to restart from last save.