I am happy to report that all of your suggestions were as helpful as they were effective--which is more to the point!
I'm not sure what finally put the little leaf munchers over the edge--but something did.
We ended up using a combination of Japanese beetle bags, coffee grinds, and soapy water (thanks, Denise, Michelle, and Rhonda!)
Unfortunately, once we had taken care of the pests, our garden was hit with late-season blight and we had to pull every.single.one of our nightshade veggies out of the garden. Fortunately, most of my non-blighted tomatoes were ripe enough to go from green to ripe on my kitchen counter. After all our garden plagues this summer, I'd say it's a good thing we don't need to rely on our own abilities for sustenance.
All these early Americans we've been reading about? It's a wonder to me that they didn't all starve to death--or at least the line of gardeners I'm descended from!