I think it makes a great daily, very capable yet still have a level of comfort most performance cars don't. Mileage is not as bad as you read online people like to exaggerate. Yes i can probably get less than 300km on the track, But on highway trips I can average less than 10l/100km if I wanted too. With my mixed driving I average 12L/100km. Slightly more when i keep my foot in it longer. Its the price you'll pay for the last n/a v8 from BMW. Also keep in mind that the low fuel light comes on at 1/4 tank, which is higher than most cars. Some people claim that they only got xxx miles they probably drove the snot out of it and considered the tank finished at 1/4 tank. It's not that bad in my experience.
The M3 is a great all around car and I think makes a great daily. I'm surprised at how well it soaks up bumps yet handle so well. They really got the balance perfect IMO. It's more practical and probably rides better than your 911. I don't know about carrying a dog in it though, unless it was a small dog.
Haven't driven in the winter, so I can't comment there. But I'm sure it's fun with a proper set of snows.
Quote for Jeremy Clarkson "its civilized, quiet, normal and brilliant,...then you can drive it like a complete hooligan"
From this episode.
Top Gear The Worst Car in the History of the World