I'd probably be driving an E30 or E36 M3 if I were that rich... and I'd have an E150 for a work car. I personally think that the E150 is more luxurious than most cars costing twice as much (and I've ridden a couple) and the premium amount of space and sheetmetal would allow me to armor it a bit and install a pretty spiffy office inside, complete with wireless internet consoles, refrigerator and picnic trays.

Then I'd use the old M3s on the weekends. They're perfect. Classy, unpretentious, quick enough to be fun, but not so powerful as to be ostentatious or gas-guzzly.