Sorry but sign written vehicles are very beneficial for corporate branding on a nation-wide basis. examples would be Royal Mail, Warburtons, TNT, Parcel Force etc.
As for a small independents Its not really worth bothering with, you may get the odd 1 or 2 jobs a year but no more.
But, and I do say BUT, this business is all about pride and if it makes the owner and the owners family proud, why the hell not!!