How many Spring Training games must be played for prospects to get the affects on development? 

I know it is not based on at bats or innings pitched but rather on games played in, if I am correct.

Thanks

None of us knows for sure.   I play my top prospects a lot.   After all, if they fatigue during the season, I can rest them.   

Ok thanks, I wasn't sure if there was a specific number. But it is correct, the number of games is more important than innings or at bats?

I have had a customer support ticket mention that games are what is factored in, not necessarily innings or at-bat's. I'm not sure that I take that as gospel though.
And I don't know if there is a certain target or goal number for either. Play your minor league prospects for sure (like Mike mentioned); don't fatigue your major league guys (and I'm not positive there's any benefit to playing major league guys at all).

Veterans, particularly older vets, who get no playing time in spring training may see some slight regression of their ratings.