Sign written van definitely pays for itself.
My last van was sign written from day 1, had it 5 years and had all manner of enquiries from it, from walk ups to people ringing me to say they had just seen my van and would like a quote.
Had my current van for just over a year and decided not to get it sign written as to busy. There has been a clear difference in the amount of walk ups and enquiries.
Without your 'brand' on show people don't know who you are and are immediately less likely to trust you. You could just be some pikey from the nearest caravan park.
Because of my change of direction in the new I'm definitely getting my van sign written again, along with new website, new logo etc.
You don't need to go all out on sign writing, something simple such as your logo, what you do and contact details is all that's needed to bring in work.