I would consider the Return on Investment (ROI)?
“Marketing and Advertising is supposed to build an argument for your business that makes your prospects draw the conclusion that they would have to be an absolute fool to do business with anyone else but you, regardless of price.”
Can you really get that message across on a vehicle?
Would you be better off doing a direct mail, fax or e-mail campaign for the money spent. Vehicle advertising is Fortune 500 advertising at its best. Will you be able to track any of the new leads you get were a direct result of the advertising? I would hope so...other wise how do you know your money was well spent.
In a nutshell, marketing & advertising is the argument you build, the case you design, and the reasons you give why a prospect should do business with you.
Envision your marketing situation as a court case - your prospects are the jury, you are the defendant and you must prove to them without a doubt that your product or service is the most practical alternative amidst all the competition. Again, is your logo/ branding on a vehicle going to do this for you?

__________________
We Create A Complete Marketing System Built For Your Company That Includes All Development Of Lead Generation, Advertising, Sales System, Staff Training And Implementation Of The Entire Program.
http://www.johnuhrigconsulting.com/