I am not sure what this weight we are talking about is coming from. I just weighed the spare and mounting hardware and then my full size spare. The spare and hardware was about 27lbs. My full size was about 70 with the new bracket.
Assuming the whole door is around 300lbs, that is an increase of around 12.5 percent or so. That is not significant at all. Even if the door was 200lbs, that is still only around 20%, still well within engineering specifications.
The real concern would be departure angle, which I believe you would lose cladding first, and as Tom said, for the once in a lifetime need, you could always remove the tire right quick and clear your obstacle. A PITA, but you might do it once...ever.
Jack, is that a better presentation...LOL.