Ian, I wouldn't worry about the business cards, I don't think may people would avoid a small company just because they're business is in transition and the old business cards don't match the website logo, just use them up and change the next batch.
A quick question, assuming a random selection of strangers read your brochure while waiting for an MOT to be completed: do you think that a) most of them would have any idea what detailing is? look at their paint work afterwards and think "oooh I have swirls/holograms/scratches, I need to give Ian a call for a detail!"? Maybe expanding the brochure to cover what detailing actually is, what common problems are and how they're rectified might draw in people who had never even thought of it before?