From what I've seen the effects of these foods is AOE, meaning that all members of your party (?) near you get the effects of your food. I'm not sure if it overwrites their food, or what, but it makes them unable to imbibe their own food, so be careful when using it. I believe they all last 3 hours.
I would probably check AH for activity on those dishes, see if a lot are selling, and how much, calculate profit and factor in chance of HQ. It seems like the stewpots are nice, although they don't add str/dex/vit/int/mnd/chr/agi boosts, they do give straight up attack+ or defence+ and that +10%HP boost. And it doesn't stack so it lasts 3hours. I would imagine this to be a great solo/farm food for higher level jobs.
If everyone followed your logic with new things they would never become widely used...since they aren't brave enough to put any on the market for people to try.