I think of my vegetable garden as one big science experiment of the kind that I was not allowed to do at home when I was ten, on account of the colossal mess I generally made. (God, adulthood is wonderful!)
I'll plant a bit of the tried and true in my garden, but my real interest is vegetables so weird, some of them can't even be found in Elizabeth Schneider's great giant encyclopedia, Vegetables from Amaranth to Zucchini.
Some of these experiments work. Some of them don't even bother to poke their heads above ground. I imagine the seeds stirring briefly in the soil and then grumpily turning over and going back to bed, muttering, "This is not Sri Lanka! Are you out of your mind? This is upstate New York."
Fortunately, there are experiment enablers, seed catalogs like Fedco, Baker Creek, and the giant Seed Savers Exchange that allow me to come to informed conclusions such as, "Red eggplants are pretty, but too seedy to be really useful in cooking." (I tried three different varieties this year, including the extra-exciting but foul-tasting 'Cannibal Red Tomato Eggplant', formerly used to sauce cannibal meals.)
As much as I love my farmer's market farmers, I could not get information like this from them. They are not mad scientists. They can't be, really. They have to grow what will sell.
By now, the value of keeping the genetic diversity of vegetables alive is well-established. And to a great extent, that will be up to gardeners. Seed banks, as important as they may be come the apocalypse, cannot possibly preserve every variety of every edible plant. Check out this great 2007 New York Times piece by Elizabeth Rosenthal about the struggle to save unique Italian varieties that threaten to die out with the elderly gardeners and small farmers who maintain them. The scientific term for these ancient vegetable varieties developed over many generations without the assistance of lab technicians is "landraces."
Of course, I'm only really contributing to the cause of genetic diversity as a consumer. I'm not out there collecting old varieties all over the world and saving the seeds of the best plants for future generations. I'm in here in the kitchen, roasting or sauteing the diversity.
But I am supporting the people who do save these unique varieties. And totally, totally amusing myself in the process. The seeds of some weird unfamiliar vegetable? Absolutely the most fun, legal or illegal, that anybody can have for $2.