Some owners of empty buildings with big shop windows are allowing them to be used as temporary art-gallery space. The alternatives seem to be leaving them vacant and renting them out essentially as billboards.
Whether or not the gallery-space option is preferable for the owner of the building, it’s clearly better for the owners of neighboring buildings, and for the entire commercial district of which the building forms a part. This is a classic “external-benefit” problem: easy enough to resolve when there’s a single beneficiary – orchard owners are happy to pay beekeepers – but hard when there are multiple beneficiaries because of the “free-rider” problem.
Encouraging this sort of activity is a natural role for Business Improvement Districts (associations of building owners given taxing power to promote local amenities) and for city art departments or arts councils. Somehow I doubt that the National Endowment for the Arts will show much interest, but it should.