I want something I will enjoy but will be slightly less precious about than my M3. It was already an expensive purchase for me, now that it's supercharged it's become, for me, a very expensive car in terms of value and what it's worth to me personally, and I'm just not the happy when I leave it in the supermarket car park etc. That's not to say I would neglect whatever I bought, but I would feel slightly less anxious about a car that's 1/3 or 1/2 its value and that I haven't spent a lot of time and effort making my own. Regarding the M3, if you're talking about the E46 it's a good car but I've never really wanted one all that much and they rust quite badly (I had an E46 330i), the engine has a lot of problems (VANOS, head gasket, rod bearings), the rear subframe is a huge issue (if it's fine you have to spend money on preventative maintenance, if it's not you have to spend a lot more money on repairs) and it would be expensive to run properly. I like the fact that on the CLS, for example, the engine and gearbox are tough and there's "only" Airmatic and SBC to really worry about.
I am a girl, I am single, no kids, no pets, so I am buying whatever I am buying because I like it
I don't need something as big as the CLS, but I think it's a very-sexy looking thing and would love to own it. The same applies to the SL and SLK. There are no requirements here, it's just what I like which is why it's quite a mix of cars I've chosen