Don't forget that the better gas mileage of diesels more than offsets the difference is cost at the pump.
Friend of mine recently "upgraded" from a '86 420 SEL to a '94 740iL. The thing he really upgraded was his expenses and repair costs. And he owns his own repair Shop
First his radio broke - $850 for a face plate. Recently his trunk latch broke and he was hesitant to dig into it because the electrical schematic was so complex. Called the dealer and they could not get him in for 2 weeks so he took a chance and it worked out fine. I almost bought a 740 about 4 years ago and am real glad I did not. I was real turned off from BMW about 8 years ago when I looked at a new one to lease and they told me that the first 15K service would cost over $1500 min.