> For example someone with bad osteoporosis, and who doesn't have a $10K+ wheelchair and a $75K minivan to carry it, won't really gain much by theoretical ADA sidewalks if the distance is too far.

You can't exactly escape the cost issue. The alternative you present is that this person has a car, which is quite expensive itself, and presumably someone to drive them given the bad osteoporosis.

Regardless of the design of your hypothetical city, such people may just need family help or public assistance to get to where they want to go.