The 335i is a great car and probably one of the best 3 series to date. However, none of us have seen any solid performance numbers for the new M3 so we have no way to judge how much better the M3 is over the 335i. My guess, the M3 will run circles around the 335i but we will have to wait and see.
What your saying is along the lines of what has been said about the Porsche GT3 and 997S. The 997S is so good now, is there really a need for the GT3? My answer, hell yes...