The e9x has proven to be less of a pain than previous M3s. It is still an M3 though and if something goes wrong don't expect it to be cheap.
These questions pop up at least 2-3 times a week around here, and it is 100% a personal decision. Some people have had poor experiences in the past and vow to never own a car out of warranty. Others either get lucky and never have issues or over maintain their car so they don't worry about it. Really the choice lies in your hands and should be made based on your personal tolerances/ability to deal with headaches should they arise.
It is a good sign that if you look around the forum you will not see as many horror stories as you would with many other cars. BMW did a great job with the e9x M3.