GreenToaster,
Your cars have a lot of character but obviously you're looking for a way to make them better. From what I can tell, you have the modeling skills. When I was trying to improve my modeling skills I'd just start out trying to build cars that I love. Since I'm into "hot rods" I usually start out with a car and modify it. My personal example would be this post http://www.giantmonster.tv/giant/?p=20.
That's how I approach the modeling side.
The other skill set to develop is bringing the images in your head to life (in drawings or in 3D). For some that's easy, because they can "recall" those images very clearly and project those images into their "canvas". So modeling or drawing becomes like tracing. I sometimes have that vision and I can work from that.
In addition when I start building or designing anything I do research on the cars that I want my project to be "inspired by". Now with the web this type of research is so easy. Just do a search online and find some inspiration.
This reference work helps solidify the idea in my head. I'll draw sketches and even build up something in SketchUp. All this effort is working towards this vision in my head, refining and building up the concept.
The suddenly. Viola! It's done.
Here's a book that a friend of mine (who graduated from Art Center in automotive design) gave me a while back.
There's some great things in it. Not saying that you should get this specific book, but there are plenty of vehicle design books out there. Any one of them could help you.
Have fun!