Here are my thoughts: meh.
Okay a bit more detail. Some wondrous excellent food granting health and life and crap seems like a fitting medieval viewpoint. Nutrition is important. People in medieval times believed all sorts of weird stuff was good for them.
Story wise I would think a resource like this would lead to conflict/stories. Faeries being the obvious ones.
Balance wise I'll compare it to a high magic theory muggle making a specialized lab for Longevity Rituals.
At M.T. Three you could add elementary, greater focus, and two greater features for a net of +6 to longevity rituals in a regular sized lab. If it was more along the lines of a large dedicated room you would throw in Spacious, Well Insulated and Well-Stocked or whatever they are called and another greater feature for +9. Refine it three times and increase the size a little more and we throw in two more greater features. For +15 Add in priceless and precious ingredients, and some nice tools and equipment and we add like +9ish more. Toss another feature and refinement in and we're at +25ish. And now we have roughly the same benefit. To decrease upkeep you'll add some missing ingredient flaws for everything that wouldn't be used in longevity rituals. Its an investment on par with a large expensive specialized room in a modern hospital. 5ish man years of expert labor.
Except the magic theory guy can wander off to make another specialized lab for any other activity he wants. And magi could presumably train under him to scale up their M.T. too.
Now, when we take into consideration Blood and Sand and their "errata" on excellent items needing to be customized I think a lot of magi/companions wouldn't let their diet be dictated by a Savant type, so this is totally a bonus that might get ignored by a character. Can you really see Cecilio doing that?
So tl;dr: Make some stories out of it, and let people choose if they want to use it. Everyone wins right?