Well, thanks all for your input...and I'm pleased to say I've gone and made a decision, and paid a deposit on a car I'm picking up this Thursday. I went petrol after considering the fact that it was over £1500 cheaper than lower spec'd diesel models, and the dealer is taking both my C4 and my old Skyline in p/ex leaving me an affordable amount to pay. The car is a silver Merc C180 Kompressor sport estate, with the auto tiptronic box, on an 05 plate, with black leather interior, full merc s/h, the roof rails....everything I wanted. My Thule roofbox will go atop nicely, and all I need is the towbar for the trailer. I'm happy!
Will no doubt post pictures of it over-filled with camping gear at some point!