I think if you are using any vehicle for work and work for yourself in the current climate you do have to think 'what impression of me does this give' and look what our base criteria is which by the sounds of it is 4wd and a decent amount of space, I am very conscious of this for consultancy work I undertake these days and low running, fuel and maintenance costs are key for me.
I agree, it's nice to turn up to a client's house in something decent. When I turn up in the Golf, the husband usually get's quite excited and it gets some good banter going (most of my clients were 80's yuppies at some point, and usually owned a mk1 or Mk2 GTi or both). A tidy Audi Allroad looking completely standard has got to be better than turning up in a Transit Connect, hasn't it?
....It depends what business/profession you are in.
The same applies to what you turn up to a new potential client wearing. Creatives don't usually turn up in suits for example.
I once turned up at Grosvenor House (Park Lane, London, in case you don't know!) for a meeting at 9:00am Monday morning to present design proposals to the board of directors of Trusthouse Forte (I had been introduced by Lord Charles Spencer Churchill) - I was on a bicycle and it was wet and I had on high-viz wet wetwear. It was a competitive pitch and I won the job which then entailed a world trip art directing photography and designing and printing a brochure for Rocco to impress The Savoy shareholders.
On another occasion I was invited to The Duchess of York's (aka Fergie) parents house near Basingstoke to present myself for a project. At the time I was running a very beat-up Talbot which I never bothered to wash and which had a big bumper sticker. I parked it out of sight outside the high wall surrounding the circular drive at the house's entrance door. When the Major walked me to the door after our meeting he couldn't see a car and so asked me how on earth I had arrived. I explained that my car was beyond the wall and to my initial horror he out of courtesy walked me to my car! I tell you, it means diddly-squat. If it does mean something to a client, then are they the sort of people you want to work for?
So, my advice is to hell with what you think the conventions are - Just be yourself and not what you think people want you to be. In my not inconsiderable experience, clients will respect you for it and also remember you.