Well, I'm still learning, and I've been hitting the tutorials like crazy. All I can tell you is to play with color speed, weight, and transform color on each different transform. I know that is pretty vague but for me it's still hit and miss, I have more unrendered pieces than rendered for that exact reason. I did take a look at some of your renders and they are really nice, there seems to be a more graininess than necessary tho. What density are you rendering them at? I render mine at a density of 10,000, the colors come out more solid with a higher density. It can take a long time to render at that density so you have to be patient. This piece took 28 hrs to render.
yeah, definitely bump that number up as high as your computer can take. 2400X3000 at 10,000 density is the most I can push my computer. 10,000 doesn't show in the drop menu but you can type it in manually. Good luck