How tall do you want it to be? Something like Serviceberry (Amelanchier) creates a very light and open canopy.

Did you consider honeylocust, yellowwood and kentucky coffeetree? I'd say these are amongst the most desirable of the leguminosae.

I'm not really looking specifically for leguminosae. Honey locust sounded really good, but after reading about the webworms, borers, etc. I guess I'm going to pass. I don't think my soil conditions will work for the yellowwood and the coffee tree may be an issue with poison pods, leaves and my puppy.

We inherited all these plantings: I have only one real shade tree, a Japanese maple in the back of the house in an area we don't really use. A side yard deciduous tree is a tulip magnolia in another inconvenient location. The mature trees here are otherwise evergreen and narrow--crytomeria, holly, cedar and giant arborvitae. On the south side is a huge, ancient kwanzan cherry with such low hanging branches you can't use it to sit under. I'd like something that actually shades the walkway and a part of the front yard and something for the west facing the kitchen stoop in back of the house (very narrow backyard area of perhaps 12 feet wide.)

Why the previous occupants never planted for usable shade ( over a 40 year period !), I don't know. Perhaps they never spent time outdoors.

American elm is known for its dappled shade. If you get one you would have to get one of the DED resistant cultivars like "Princeton".

8 years ago, I planted black locust "Frisia" at the curb and have not seen any suckering. It's well over 30' tall now. Mine was grown on its own rootstock, not grafted.

Look at Halesias. Some get pretty big--30 feet or so--and have lovely bloom and dappled shade.