I think you should do a bit more homework before labelling people as fools....There is no way Z4M prices will end up as the same as Z3M prices. Is the Z3M not a LOT rarer? The Z4M, whilst great, will not be as iconic; and only a fool would base his assumptions on future values on this.
There were 165 RHD S54 equipped Z3Ms, and they were only built in 2002. There were about 300 of the S52 variant built between 1999 and 2001. Z4MC production for the UK was 588. The Z4M is already considered a future classic by various sources - Evo Magazine for example, though their write up is a mess! - and represents one of the last of the 'back to basics' , NA, manual M cars.
The M costs more to run but having driven both, its more car. The costs are tiny compared to some cars - it's all relative. Besides, nobody buys a ten year old 'normal' Z3 Coupe 3.0 over a Z3M Coupe due to 'running costs'.one will they choose when the 3.0si is massively cheaper to run than the M. Even when compared to running a Ford Focus, the 3.0si fairs extremely well.