There's a lot of quantifiable benefits already described, carbon and water storage are at the top of my personal list. Deep-rooted native plants (compass plant, lead plant, prairie clovers, etc) are able to pull nutrients from deeper in the soil profile, increase water retention, and provide more diverse nectar sources across a broader flowering season.
I think one of the big values of small plots is as a teaching tool. There's a local non-profit that's big on the "farm your yard" ethic- they develop community gardens, put in demonstration plots, offer classes on gardening and processing (Canning, pickling), bees, backyard chickens, troubleshooting pests organically. They've demonstrated to the public you can grow produce as good, or better, than what you can get in the store, without trucking it in from southern California, or using a ton of herbicides and pesticides. They've put small plots to use in terms of production as well as an educational resource, and it's really paid off around the community.