Im glad you've found something that works for you, but you must understand that you have quite the unique circumstance there. There is no gardening out there that would ever be able to replace the exercise that I do...gardening is extremely mild cardio at best. And 300-800 sqft of sun-exposed space per person in the city where I live would undoubtedly cost an order of magnitude more than I currently spend on food.

If it were really that easy to grow one's own food, industrialization would have never happened.