Given how fast technology is progressing, I wouldn't keep one of the newer BMWs forever. Not only are the complex computer systems hard for most indys to fix, but engines are rapidly becoming more efficient.

Prior to the MOST-BUS system (E46, E83, E53 etc...) stuff was pretty easy to diagnose and most BMW independent shops have the resources and tools. Since then, a LOT more computer-dependent diagnostics and parts came into play and the operating software is horrendously expensive. Hence why the E9x depreciates like a piano off a building once the warranty runs out. E70 will probably do the same, if not worse given its greater complexity.

Combine that with rapid improvements in efficiency and reduced emissions, it'll only be 5-6 years before a vehicle is completely obsolete. My X3 isn't even 10 years old and the new X3 xDrive20d makes the same power, more torque, better acceleration, yet consumes half has much fuel and emissions. From a 4 cylinder............diesel! Makes my X3 seem like a caveman.

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2014 Mazda 3 GT: Ø Consumption: (click for details)