I have a 94 camry and use it through the week to commute to work and back. It's also great to take on trips to my parents house, without worrying about adding 160 miles to the m3. 100 miles a day is a lot to be adding to an m3, and will lower the value overall. It will make your travel time very enjoyable, but the cost of replacing basic wear and tear items on the bmw isn't cheap. Tires in 235x40 are typically 200.00 ea for the sticky ones. If you can afford to keep the toyota I recommend you do it. I drive my camry whenever it rains or snows, and it makes every moment in the m3 that much more special. IMO I think you should keep the corolla as a daily driver and use the M3 on those special sunny days :)