I guess sometimes having a crappy week day car makes for an even more exciting drive when you get a chance at weekends, you clearly love the Do-luck Sup and in your eyes it is the Ultimate Supra, but you really do come across as wanting to upgrade your everyday life (wife included) and doing that will be more satisfying than having your dream car in your possession. It's a tough call but atleast you have a well documented memory of reaching your target car (epic trip to collect her/him), and let's be honest most of us don't manage to buy out dream cars, but from a distance (where I am standing) it looks like you are one of the lucky few that have been there and done that.
You have a nice family dynamic going on and I can see they mean a lot to you, so my honest opinion would be to let her go for the right price, and if she does not sell then it was not meant to be, and you can take it as a sign that you were supposed to keep her.