Well today's safety regulations that are pushed by government agencies and the industry itself through competition among car makers would never allow BMW to build a lighter car. If they take equipment out they'd either not comply with some safety regulations or would shoot themselves in the foot against competition from Benz, Audi and the other big names.
And as for building CSL versions standard it's a good idea. The only reason why I think they don't do it is because whenever they do take a load of stuff off the car to make it faster they want to charge MORE for it even though you get less value for your buck. So in other words they are effectively ripping you off and they can only do that on your face and in bright daylight if they have the excuse to say that it's a limited production run "future collector's" car as all of the CSL/LTW cars are.
So I say if you want better performance the only thing you can do is buy the standard car and rip stuff out of it at the expense of ruining your warranty