Dickey is coming off a 3.6 RA9 WAR season, makes 12M, requires only a 1 year commitment, and has no draft pick tied to him.
Gallardo is coming off a 2.5 WAR season, just declined 15.8M, requires at least 2-3 years, and has a draft pick tied to him.
I don't see any scenario where Gallardo over Dickey makes any sense, unless you think that the Dickey return package would outweigh the draft pick and any value difference.
***Used different WARs since I think each represents their respective pitcher better.