I see a lot of good ideas here and some of them I haven't even considered myself.
sdiver68, I see where you're coming from. I too see the 335i as the value play and I might have to resort to it if the M3 does start at 67k. (Well that opens a door to lots of cars, i.e. preowned cayman s, 335i, 135i and perhaps the low end of GTR and Supra.)
I am an engineer and I see the satisfication of building a beast of my own but reliability usually takes a dive. To be reliable, the aftermarket engineers really need take top down approach. Derive their parts from a system level specification and then engineer their products. However, my guess is they are doing a bottom up approach by building the products first and then stress test the system. If things don't break they will sell the product and if things do break then tweakble the settings.
For installations you have to take the car to a reputable installer to make sure everything is installed correctly. (I can do ecu, brakes, and most fuild but I don't think I can install LSD myself.) And then there is the issue of taking the car in for warranty service. All in all that's too much hassle for a daily driver.
But boy everytime I see this picture... I want a m3. 8 is greater than 6 no matter how much boost that's going into the 6. Just imagine a turbocharger for the 8, which I won't do because of reliability.