In addition to blueberries (don't forget that there are non-commercial varieties that are WAY WAY better, just need to be cultivated) you could also add highbush cranberries, Lingon Berries, some varieties in the Raspberry family like moist areas too (Salmon berries are fantastic and prolific in the rain-forest here in AK).
Something I know also can work for you if you are ok with some animals are fiber animals. Sheep, Angora/hybrid goats, Angora Rabbits, Llama, Alpaca (though camelids are expensive to get into, and probably not worth the startup costs). You don't have to process the fiber for sale if you don't feel like it. I know plenty of spinners/felters who will buy it raw and process themselves. You can also sell lambs/kids/other babies for pets, or (depending on breed) sell animals for meat. Since you already have a dairy barn, you could go into goats milk! Depending on location and demand, there can be a premium on goats milk, or products made with the milk.
All that said, count me among the jealous of your space folks! About 20 acres is my ideal, though probably not in the Midwest. I like Alaska too much.