So far as spring training goes, it depends on the team and its following. Vero Beach used to receive nearly a third of its tax revenues from the Dodgers spring training (now dependent upon over-development and outlet malls since the Dodgers left and the Sunkist Orange grove has gone condo). Jupiter doesn't depend on the Cardinals, though the Cardinals do bring in a huge amount of revenue with their fan base (which usually draw 2 or 3 times that of the Marlins, which share the facility). Spring training facilities often draw more hotel room nights than the major league parks.
As for the secondary uses, the stadiums are used for the minor leagues and for tournaments during the minor league all-star break and other times during the year. The larger facilities have tournaments that will draw 200 teams from all over the country, and can bring another 25,000 hotel room nights. There are few non-baseball uses. However, there is a huge difference between spring training facilities and other minor league parks. Spring training facilities are several times larger, and in addition to the stadium, the better ones usually have several other full-size fields, a few smaller fields, massive bullpens, what amounts to a golf course cart house, etc. All the fields need maintenance every day of the year. The Nationals facility in Viera is/was one of the smallest in Florida. I think it has only one other full-sized field and one smaller one for infield practice. Most others have at least 4 full-size fields.
