is it worth swapping 10.7 inch discs for the 11.8 inch?

The reason that i did the 11 3/4 inch rotor conversion on the 71 Cuda, is because it needed a front brake job, and the rotors were already at minimum thickness, and wouldn't take another machining, without being undersize, discard, thickness.
I already had 15" inch Rallye Wheels on it, and had a pair of spindles, and new rotors, and the taller caliper mounts, waiting to be used.
So i did the swap.

If you have the parts on hand, then go for it, but if you have to purchase everything, then you might want to think twice about doing it.
It will be a diminished return, on your investment.