I have a Martin D-15 and a J-15 which are incredible sounding guitars although very plain looking (all Mahogany)

I think the would really look nice with a simple cream binding added which would not affect the tone at all. Shouldn't be all that hard to rout out a binding channel and glue one in.

Any one do this?
I wouldn't.

Adding binding won't be all that straight forward. Acoustic guitar tops have a slight radius, so when cutting the binding rabbet the router cannot ride on the top or the depth of the channel will be uneven.
To be able to cut the channels you'll need a jig that indexes from the guitars side or keeps the router at right angles to the side.

All this will be alot of work, not mention any chipping in the finish that may occur during routing.

Some makers believe that binding on acoustic does change the tone.