As others have stated, what a sad end to your love affair with your QV.
Have never owned an Alfa so can not comment on dealer performance, but my experience with my local BMW dealer suggests you should be just fine with your M4. I don't know whether it's that I've never owned a 60k+ car before this one, so didn't know what to expect service wise, but I have had niggles with my 6 and the dealer has rectified everything with no hassle, unlike my Jag and Volvo before it. Personally I think dealers should offer a great service whether you are buying a basic spec Mito or fully kitted QV but that obviously doesn't always work out.
My father has a Lexus and even though he has never bought a car from them and probably never will, the service he has had from our local Lexus dealer has been top draw.
I would definitely be firing off some emails to management, you never know, one of them might just care enough to make sure this doesn't happen again to an Alfa owner.