Nav is a "must have" on the coupes. It is not so much of a necessity on the Roadsters.
The opposite applies to heated seats, not a must on the coupe but if you want the roof down 3 (or even 4 lol) seasons per year on the roadster...I would never buy a roadster without them. Very difficult to retrofit.
The standard stereo is absolute pants on either model.
Wind deflectors, bluetooth and cruise control are relatively easy to sort out if the car you buy doesn't have them.
These cars do not resell very well once mileage gets above 45-50k, because there are just so many low mileage examples. You will find a proportion of cars are kept as 'second cars' more so the roadsters.
I wouldn't go for an absolute basic specification but something with a couple of options. It will come down to the difference between a car with Nav or without Nav, as that makes the biggest difference to prices from what I can tell. The screen is very difficult to see on a sunny day with the roof down anyway, plus in my case I already had a top of the range TomTom which has a lot more functionality than the BMW Nav.
Personally I would (and did choose) no Nav but lower miles; when purchasing cars I consider mileage, condition and an enthusiast owner over spec. This last point is the key advantage of buying privately (or the key risk buying from a dealer).
The pre and post cat lambda sensors on the M tend to need replacing in the first two or three years, not on all cars but seems a common fault, less so on cars not used year round or in the rain because one of the contributing factors seems to be road crap thrown up onto the sensor. Cost about £250-300 out of warranty. People that have had their sensors changed don't seem to have experienced a problem since.
It's the same engine as the M3, well proven, some initial bearing shell issues in 2001-2 were ironed out long before the Z4M was produced. I have not known anyone to have a clutch changed on this forum as yet, and I never recall seeing an M3 for sale with 'recent clutch change' in the advert. I surmise that they last a long time compared to some other performance cars (STI for example).
