Hi thanks for the welcome. I had originally joined as I was trying to get into a Z4C myself but ended up sticking with my 130i.
I've always been wary of a sparkling clean engine bay when buying a car. I won't let it get to the stage where it's horrendous, but as a buyer myself it's much easier to spot oil leaks and see what has been changed/messed with in an engine bay that has not been cleaned fastidiously.
Perhaps the ad doesn't make it clear but if we've had problems with the car then we've had them sorted e.g. the O2 sensor, the coolant expansion tank and we even got the rocker cover gasket replaced as "preventative maintenance". In fact a lot of the pipes for the coolant system have been replaced as the coolant dumped all over the road soon after we got it, this means that a lot of the brittle plastic bits under the bonnet are new and are fit for many years/miles to come. And on top of all that I ensure that both this car and my own are kept in good working order, i.e. I take my 130i on track so it needs to be in great condition, whenever I'm working on that I give the Z4 a once over too.
As you say, it's a good car for someone and if it doesn't sell we won't be disappointed either!