Agree with all this, for the most part. I think the investment we've made in Wilcox (3rd round pick just last year) means that a guy would have to be far and away the BPA in the first couple rounds to justify a pick on a S.
Getting to the 3rd round though, I could see taking a guy we had more of a 2nd round grade on. Let's not forget, defense isn't played in black and white. It's played in grey. What I mean by that is we could easily get Church, Wilcox AND one of these highly rated rookie S's on the field all at once in certain situations. Let's say we draft Brooks and believe him to be a true FS upgrade. 3rd and 10 comes... Brooks at FS, Wilcox at SS and Church up in the box in place of the SAM. The nickel is played with an extra DB, but there's nothing that says that extra DB has to be a CB if the matchups dictate otherwise. I guy like Ward also seems to be a slot CB option if Scandrick goes down.