It was the best money I ever spent on advertising by a long shot,.. don't even hesitate.
best thing i ever done, ive received a number of jobs, conny roofs, gutter clearance, new regular customers etc etc
i think you do need to make it look professional though, and it needs to stand out, you see a lot of vans around that look really pikey
you dont need to pay the earth either, if you've got a bit of an imagination & dont mind putting it on yourself which is really easy, you can design your own, i did, i used
http://www.thesignbuilder.co.uk/ i have a swb transit & for both sides + back n front for £129 inclusive
it helps to have a nice clean van as well.
also if you haven't got already, consider getting some uniform printed, that gives a good impression to, again you dont have to pay the earth, i used to spend a lot on getting tee-shirts & sweatshirts printed. but now i just where a printed hi-viz vest over whatever i am wearing costs less than a fiver inc print off ebay
definitely go for it
tony