I have a 2011 e93 and I love it. It is beautiful and fast and I would not be concerned about the difference in weight or trunk space. IMHO there is little difference in trunk space between my M3 and 335d when the partition is up.
You need to decide if you want a fun car or a practical car. There is always the option of having 2 cars-an M3 weekend car and a cpo pos as your daily driver.