Hi Chip,
I've stayed CR 14th floor concierge but I've never stayed on the 12th floor. I think the difference is that the 14th floor has an actual concierge lounge that has a big screen TV and food and drinks are served from breakfast through 10:00pm. It also has 2 balconies that overlook the MK so no matter where your room is you can still view the fireworks and the MK from a private balcony. Also, the elevator area is grandly decorated with a marble floor. The concierge staff really made us feel like kings/queens. The rooms on the 14th have a larger bathroom and balcony but make up for it by having a slightly smaller bedroom area. There's no day bed in the 14th floor rooms. Each room has a fridge that is stocked daily with water, juice, and soda.
If I'm not mistaken, the 12th floor doesn't have a lounge and it stops serving food around 4:00pm. There's a fridge in every room but I don't think they stock it with drinks.
I was lucky enough one time to get a free unrequested room upgrade to the 14th floor concierge. After that I stayed 2 more time on the 14th floor and it was really expensive. I don't think it's worth it for us any longer but everyone is different. IMHO I would really evaluate whether staying 14th concierge is worth the extra money for you and your family.