Amazing stuff! I really love to grow them from seeds that I grew myself, as some plants like amaranth and wild rocket and salad rocket produce so many seeds. And when you try and separate all the chaff from the seeds, it is sometimes easier to just plant some of the leftover chaff for micro-green purposes!
And you said something so true, few people think about using bulk wholesale whole spices (aka seeds) such as mustard, fenugreek, celery, and so on, for growing produce. It is way cheaper than buying small packets of seeds.
Maybe I should also start selling my seeds, as I have literal bottles and jars full of the stuff; way too much for my small scale growing operation to ever use.
Selling the seeds you harvest from your own plants sounds like a great idea too me!! That is actually something I dream of getting into someday. If the mainstream economy ever does break down (though I hope it doesnt) I predict that seeds will be a form of currency.
There is a novel in my home language (Afrikaans) that deals with this very topic! It is a dystopian novel where seeds are a commodity and growing food has become a forbidden secret. One of my favourite modern novels. But I am sure this already happening with big seed companies already owning the rights to so many things that control the growing of crops.