Also, here's a non-intensive way to get to New123455's original post:
As far as I can see, we don't want gradual realistic improvement because that would be code heavy and get in the way of everyone, even people who don't care about farming, for the benefit of a few dedicated farmers.
Instead, what if every crop had a slim slim slim chance, like 1 in 1000, to drop "good rye seed" for example instead of just "rye seed". That would still reward an attentive farmer who selects their "good rye seed", grows it carefully, and ensures that they slowly increase their stock of good seeds, but it wouldn't bother anyone who doesn't care about farming. Someone might get 1 "good rye seed" and just plant it along with all their others, not bother about it, and by doing that accidentally, very incrementally, improve their seed stock.
I think I would find this rewarding, but then again, I like gardening. At present the system is plenty complex and very satisfying, so I don't see a pressing need to improve it.