I have a friend that sales his to fancy restaurants, but unless you have the right connections I dont think you will ever be able to make a business out of guineas. I do love mine however. I started with guineas because where I lived there were ticks everywhere and I had to something about them. I havent seen a tick on me or my pets in a couple of years. They also slow down the grasshopper population. In this drought we have been in lately I think the grasshoppers are eating more grass than the cattle, but my guineas keep the ground and garden pretty clear of the big grasshoppers. I think when they get bigger they must be easier to catch but harder to eat. It is hilarious watching 10 guineas chase one that has a bug in his mouth. He's running so much that he cant eat what he caught.
I believe keeping them is all up to what you would want out of them.