i saw an episode of Simply Quilts several years ago of which the subject was quilt restoration and preservation. the expert said that when they're fixing up a quilt that's in the sort of condition you describe, they cover the weak spots with very fine, very sheer netting. it's cut and applied so that the stitches holding it on will disappear into the overall design.
maybe you could do the same. to make it easy, cover the whole thing with one big piece of netting. add handquilting to hold it in place.
just a thought.