I agree the M3 is a great balanced car, but you can improve power while still keeping balance. Again, this is why these things should be done by reputable tuners/technicians. If you increase power, you should also increase braking etc… for instance, a stroker kit would certainly not add any weight to the front of the car (in fact maybe even reduce weight and balance is kept equal), but it would take you to say 520 bhpīs (a huge increase in power IMO), you can also add a BBK with light weight wheels that will improve braking, reduce unsprung weight, and improve performance, etc., etc… you get the point.
A trubo kid would be much trickier as you would be looking at some added weight but would have to seek to distribute this appropriately and in any event, if done very well and skillfully, will not decrease the carīs “curbing” performance (look to the GTRīs weight/performance ratio for instance).
Why not simply buy a C06? Cause the M3 is a great platform to start with (great chassis/engine) and I love the M3 and don’t the C06.