AS for the weight of the E90/92 M3; I would not worry too too much and here are some reasons.
BMW seems to introduce certain items in a limited spec edition at the end of a series and test market perception and client reactions to this things, such as:
- Adjustable Bolsters on E46 M3 --> now in sports pack on E90
- Carbon Fiber/Composite Panels, trunk and roof on E46 M3 CSL --> Front Fenders on E92 are composite + the same for Bumper and front fenders of the new X5 (no seem)
- BFD (Brake Force Distribution) Ligths on E46 -> Now on all E90
- Corona rings
- Swiveling headlights & high beam Xenons
- Better DSC&DTC on E46 M3 -> Now on E90
- + more, but no time to list for now
One more thing to keep in mind, when BMW introduced the last Generation E46 M3, they were not in Formula 1. When they introduced the New M5 V10, they had just had about three years in F1 as an Engine supplier to WilliamsF1.
Now they are entering their second year as a full fledged F1 Team... so what does this have to do with the new M3?
This summer as the two North American F1 races, BMW had a lot of demos where the public could come and see the difference between components of F1 and other BMW race cars vs regular road car components, such as:
- Brake Discs
- Brake Pads
- Car Panels (ie: Trunk or Fender)
- Gear Box
- Cylinder Block
Let's just say that some of those components where 1/3 if not 1/4 of the weight of the regular road car component & lasted longer ... was mind blowing.
So, I would not worry too much about your future M3; the power to weight ratio is a top priority for them!
If they talk about it in the intro of the E92 ... they sure are not going to miss it with the new M3
Sorry for the long post, but hope it's been useful