Why "scout" ships? Hundreds of Star Trek episodes have proved that even a very powerful flagship like the USS Enterprise can be seriously challenged by "routine" exploration and search missions: a state of the art expensive and very strong ship should be the bare minimum for venturing in unexplored or dangerous space, with powerful groups of ships preferable and cheap small ships completely out of the question except as the numerous payload of an aircraft carrier.
Reasonable (and fun) exploration should consist of going there and kicking ass, conquering new territories and clearing them of threats; probes and instruments are a small addition to a primarily military activity. The difference with a military campaign is that exploration happens in "wild" places rather than in well known places that belong to the enemy.
Long range sensors can give a good indication of where to send the exploration duty fleets (or what important planets are going to be fought over when the enemy reaches them too) without yielding anything concretely useful.