Not too long ago I received a 135 w/ dct loaner from my dealer during service. It was a fun fun car to drive. It put a smile on my face the moment i opened it up Driving that thing made me realize how practical torque is as a DD. Based on my experience w the 135, I wouldn't hesitate in getting the 1m. Honestly though I do not like the looks of the 135 albeit the 1m looks a lot better. But the drivability and the fun factor would outweigh any reservations I have on the looks.
I still feel there is more prestige with the m3. The last true NA motor M car is special as well. Honestly it will be considered a downgrade from the m3 if that matters to you.
If I were in your shoes I would strongly consider it. The deciding factor for me would be the economics of the deal.