We had a guy at Indiana St who no pro teams looked at. He dominated 1 season of Indy ball, then he got picked up by the brewers and he ran through there organization (making a spring training appearnce with the big league guys) now he is in AA in his 2nd full pro season with the talk of him going on the 40 man!!
So I mean its worth it, it just might take some extra work and you are not going to get all the chances that a Top-10 or Top-20 round pick might get in the minors. It might be 1 strike and your out!