I'm kinda in the same situation - however, I let the wife drive the GLK as her daily. I have my Accord and Z4, both which are stick. It was a tough sell to purchase the z4 as its another car she can't drive, and she won't learn stick.
So although my Accord is great for taking the daughter around, its still a stick...so no emergency car for her. My plan is to sell the accord and just get a tsx or something, smaller and more nimble. The z4 is a diff story...I may have to get rid of it all together
as she thinks its too much of a luxury.
I would say, if you can, just get the GLK, and keep the Camry and M3...or sell both to get a 4 door auto sedan that you drive.