I remember reading somewhere about how creatures and spirits recover magic might, and I was wonder if anyone knew where that was. Also perhaps how that would interact with the Hermetic Empowerment virtue from TMRE p64?
A good place to look for Magic Might recovery would proberbly be the "Auras and Might Recovery" box at the bottom of page 30, RoP: Magic.
However, this is a recovery rate for Magic Might points, not score, which is what is reduced using Hermetic Empowerment!
Magic Might score is generally not recovered once lost. Certainly not through something so mundane as the passage of time.
That is not entirely/necessarily true:
Outside of that quote from RoP:M, take a look for specifics for at least some magic beings in TMRE and A&A. Unfortunately, I didn't write down the page numbers when I wrote those two books as the sources of the specifics.
Are you referring to Might Score or Might Pool?
Might Pool recovers at a constant rate over a 24 hour period as described on page 29 of "Realms of Power: Magic".
Might Score must be replenished by consuming Vis as described on the same page of the same book
You really need to read that page again. Both things you stated are not quite written as you describe them. First, Might Pool may recover that way, but not necessarily. Note how it references the box on the next page. Second, that bit about consuming Vis is about gaining Might Points, which means refreshing the Might Pool.
Again, see A&A and TMRE.
In RoP:M you can also eat Vis to gain more qualities, one of which is increased Might, so this is a work around.
There is also a line about the possibility of recovering 1 might per season if it is spent permanently on ritual effects, but it is apparently optional...