What do you intend to use the car for? I had the F10 550i before and now a F06 650i. And I also have an E93 M3. Also had a 135i vert before.
Very different car for very different purpose. The M3 is a fun car. Very different then non-Ms. The Ms are mean to be driven HARD. They have a whole host of sport oriented equipment that you don't find on non-Ms. For instance, all the current M cars have real LSDs as opposed to fake e-diff ones. The tracks on M cars are different then non-Ms.... etc
However, I also have 2 daughters (7+9) and I find that I use the F06 much more for daily drives with them. Just way more comfortable, not only to sit in and drive casually, but also for the passengers as well.
So you really got to ask yourself, what is your intended use of the car?
However, to give a short answer to your direct question. No, M cars are NOT OVERRATED. In fact, if you were to mod the 335i to the M3 level, buying the M3 is actually cheaper........ I tried modding the F10 550i to match an M5, just not worth it!
F06 650i Gran Coupe Ruby Black/Dakota Cinamon- 2012-10-12 Adaptive Drive/IAS/Surround View/Adaptive LED/Comfort Seats/BMW 356 Liquid Black/Michelin PSS 245/35R20-285/30R20
E93 M3 Cabriolet Satin Pearl White/CR - 2012/03/12
Bilstein PSS10/ Michelin PSS 245/35R19-265/35R19 Brembo GT
2011 F10 550i M Sport - Retired