I grow sweetbay magnolias here in Ohio (zone 5, clay soils), as well as the cucumber magnolia (M. acuminata), M. x loebneri 'Merrill' and 'Leonard Messel.' I find all of these more easily grown than the common saucer (M. soulangeana), and in the case of Merrill and Leonard Messell their early spring flowers are more tolerant of frost. Merrill is also quite fragrant, with a sweet/spicy scent. Great bee trees as well in bloom, and it's not uncommon on a warm spring day for the trees to be buzzing with honeybees and the native species.
So, could/should they have a place in permaculture? Quite possibly, if only for the fragrance and pollinator benefits. I haven't noticed any fruit tree benefits, but my magnolias tend to be tucked more along the edges of the property since many of them benefit from some shade during the heat of the day here when they're young. BTW, regarding the leaves: people who raise dart frogs and other damp habitat amphibians actually BUY dried magnolia leaves for the floors of their terrariums since the leaves are naturally pretty decay resistant.
According to Eat the Weeds (here's the link:
http://www.eattheweeds.com/magnolia-viginiana-how-sweet-it-is-2/ ), sweetbay leaves were used in teas and to flavor soups/stews, as were parts of other native magnolias, along with other uses.