Hi Tom,
Some are brilliant some are random and some are not sharp, you probably know yourself which photo belongs to the categories.
It's all about
1: having talent (you have it)
2: proper material (you have it)
3: doing it alot (you're working on it)
4: being critic for yourself (you'll do it automatically when you have to go over a billion zillion photo's after every meeting) Only keep the coolest or photo's from cars of people who asked you to photograph their cars.
The difference between a random picture and a cool picture will be in the details

Dirt flying is cool, cars crashing is cool, more than just 1 car on a photo is cool.
It has become "easy" for me to just shoot a car when it hits a corner. It is alot nicer to have that same car with the one following him in the background

.
One thing is important, try to have fun! You will never get any money for it, just give people a nice remembering of their raceday.
My pic's are here:
www.rc-offroad.be
going from my dad's 300D standard lens to a 450D to a 40D with 70-200 L f4 lens
I've just did the Euro's for the french/international website 'PetitRC' and those pic's are here:
http://www.petitrc.com/_forumphp//sh...ad.php?t=45535
Good luck !