Sort of. I use a section of the garden to broadcast a variety of mixed greens. Then let several different plants go to seed, collect the seeds and broadcast plant again, till under and wait for the next crop. The next year I use a different section of the garden for rotation. The more mature leaves that we don't consume go to chickens - they fight over Russian kale - odd how they know nutrition better that some other two legged creatures. I haven't collected/saved seeds from the mixed greens from one year to the next though.
I've started saving seeds for Mexican marigolds, peanuts, cucumbers, dill and sunflowers. It's rewarding to save a buck or two.