I'm in a similar situation to you family-wise, but instead the vehicle is a 2015 110, and I'm contemplating swapping it for a series for the reasons you want a defender!
My 110 doesn't get used much, has a lot of money tied up in it (more than I'd need for a series), and costs a fair bit to insure, tax, service et c. A series would hopefully see to a fair bit of those costs, and let me 'tinker' more than I can with a more complicated late defender.
Against all of that, I have a fairly gleaming 110 which I know well, I don't have matrimonial pressure to release cash from it, and it could just grow old with me and the family.
I get the safety issue too, but a defender isn't going to be much better off in a crash, perhaps worse even as it can reach higher speeds!
I offer this perspective only so that you can see that it isn't necessarily greener (no oval related puns intended) on this side.
Perhaps we should both try each other's vehicles, in fact?!