Steve is correct in everything he says. I may not be able to agree with him on the E30 front (never been in one) and I disagree with the slander of the SMG (I think it's great!) but he's right when it comes down to what the M3 should be. The M3 needs to be a light, and powerful machine. The CSL had 350 HP or so and at the time it was deemed an engineering masterpiece.
The E46 M3 is nimble, high revving, and a screaming beast of a car. The E92, while an amazing car too, was just too heavy. It's so unfortunate that BMW released such a masterpiece of an engine and housed it around a huge body that weighs a lot.
Honestly, I don't ever see myself selling my E46 M3. If I get the upcoming F30 M3, I might just treat my E46 as an everyday car - it's that good and comfortable. But I get the feeling that BMW will be asking for too much whilst upgrading insignificantly (or not upgrading enough to keep up with the competition). At the moment, I'm leaning towards a used GTR and keeping my E46 M3 as an everyday car.