Go for the 996! The plus is that folks, when they see you pull up, will still think you drive a Boxster
Seriously, it is a different car than the Boxster, but its still a Porsche and its still a great car.
If you think it more rational to say "the kids will fit right in" remember how big a car seat is and how awkward it will be for getting them into it. Not impossible. A friend of mine had a 964 and has many pics of his 2 kids in car seats, in the back of it.
Go for it!