[Efthreeoh]

I have an N52 with 330,000 miles on it in my '06 325i. I've driven the shit out of it too. I doubt the N52 will have any issues beyond the normal stuff that you seem well aware of.

I also have an '08 E86, being a coupe it is much more stiff that the roadster, but the roadster is quite stiff as open chassis go, so I doubt at 180K the chassis is bad. I bought my Coupe at 23,000 and it now has 72,000 2.5 years later and I have to say the chassis and interior have held up far better than I expected.

Both my cars are manuals so I can't speak to the auto, but my sister had an '04 X3 that she never did any trans fluid changes until sometime after 140,000 miles (a BG flush) and despite all the hoopla of flushing the trans at that level of mileage, it quite improved the shift quality.

The rule of thumb of high mileage BMW ownership is you must be a pretty serious DIY'er, which you seem quite capable as one. You seem not scared of BMW ownership. I've had 4 BMWs (still have 3) with a cumulative total of over 800,000 miles. Two cars I took past 250,000 (the E90 with 330K) and the 20-year old Z3 has 177,000 on it (which will be on a 8,000 mile road trip here in a few months).

If you can get a good deal on the Z4 then I'd seriously look at it. 1st step is a test drive and mechanical inspection. But there are thousands of '06 - '08 roadsters for sale with lower miles and $12K in price. Something to think about.