Is it viable to focus on light, fire, and earth to rush 1-2 upgraded gold towers early to maximize purchasing power later on? They're strong towers with good buildup, and they also allow you to have early blacksmith towers aswell.
I also find that nature is a good complementary element to this strategy. I'm becoming very fond of using flame and moss towers to weaken creeps before they get mopped up by the gold towers, and the amplify tower feels good for further boosting your farming potential.
Are there any other towers that shouldn't be overlooked when you're building early gold?