Randallneighbor - I too was shopping for a used 545i but soon found that I would have to take too high a mileage penalty to justify the difference in price vs. new. I ended up paying 60k for a new car after a dealer discount whereas the same optioned used with +/- 5000 miles are in the range of 56k. That new car smell (not to mention the certainty of it being untouched by another heavy foot) was definitely worth the extra 4k.
And as for the back seat passengers, they are a rarity as my wife drives it to work and I get to lug the kids around in a '91 Merc wagon
I did try to convince her to buy a Cayenne S, but having driven both (not the Turbo though), I am actually secretly pleased she is such an avid BMW fanatic.
ps A tip for keeping the passengers from bickering when you have to have them - gravity and fear. Serious cornering G's and some late breaking do wonders for quitening down the rabble
