I would definetly invest in a better helmet. My expirience is that you get what you paid for. Right now I got me a new shoie RF1000, and I love it. Ran me less than $300, it is much better than the RF900 I had before, and its silly to even compare it to my first BELL, which was a $60 piece of sh*t. Suprisingly, I didnt find increase ventilation in helmets such a good thing. More vents tend to cause a great deal more noise, without actually cooling me down much. To me the greatest qualities in a helmet are light weight, comfort, low noise, and aerodynamic stability. Suprisingly wind noise tires a rider more than any other aspect of riding.
As for joe rocket vs alpine star, while joe rocket is good, it is not nearly the same quality. In my expirience they concentrate more on providing a "cool" look, and a cheap price than they do on protection. That is not to say they make bad products, becouse they are good. But alpine star is better.
Personally I'm a technik (sp?) fan.