Too right, I wonder how people forget this fact - when Giggs, Rio, Scholes, Vidic, Keane etc were in their primes we didn't lose them but that doesn't mean there weren't clubs that coveted them. The only player we wanted to keep that we lost was Ronaldo but I'm sure if Fergie and the Glazers have to do it all over again they would do it differently and give him a crazy ass contract to keep him, that's what these clubs do with this type of player so you're left with Atletico, Dortmund and the Italian clubs as possible hunting grounds.
I think football judgment is more important that the player's status as the Martial signing clearly shows, you have to look at a player and make intelligent assessments as whether he can make the step up and influence your team in a manner that a Muller type does. So you're left scouting the tiers below whilst watching with keen interest any developments at clubs like Barca and Real with regard to who they are signing and who they are getting rid of and if they can fit your team - that's how Arsenal got Ozil and Sanchez.