Much as it would be a shame to sacrifice the amount of actual scenery captured on the film, I think the biggest single way of making it look more 'professional' without increasing the budget for making the video would be to have the camera stationary and filming riders going past.
Nice as it is to see the road, it would be more 'slick' if you eliminated the wobbliness caused by the fact that you are obviously holding the camera in your hand.
Either do that, or find a way of actually attaching the camera to the car in some way.
Don't get me wrong, what you've done is what I would prefer to see, but if you are trying to raise as much money for charity rather than attract the sort of people you want to attract then you need as many of the fickle proles as possible to enter which means you need to make it 'slick' and have 'wow' factor, rather than maximizing descriptive value to the connoisseur.