Since I only use the basement for storage at this point, would I gain
anything from hanging sheets of foil-face 3/4" or 1" foam from the sill
plates in the former garage bay (now buried) in the original part of the
house basement, the long basement wall on the prevailing wind side, and in
the crawl under the addition? The former garage has a lot of foundation

Yes, but you'd get more benefit per square foot of insulation with
(more) insulation the underside of the floor. Only insulate the
part you're trying to keep warm. Don't forget the stairwell and
cellar door.