Interesting advice. I get scared enough in my 3.0. And if the engine is setup properly it should almost keep up with an M, in a straight line at least. And mine is well setup now - it drove like a 2.2 when I first had it and I've done everything on it. And yes, I know straight line acceleration is only part of the M proposition. But I just don't want to sink the money in either. I could have 7 non-M Z3s for £15-£20k - oh yeah, I've got 7 non-M Z3s...IMHO. Z3M is a great car but I would go for a good solid 3.0
Fair play to anyone who wants one though. There are usually considerably more Z3Ms for sale than 3.0s. BMW made more Z3Ms and more of the 3.0s have been broken for spares.