Should the yankees focus on there farm system and not sign free agents?

Should the yanks focus on there farm system for right now and not worry about signing top free agents like ellsbury and beltran? Ok, so they don't make the playoffs in the next couple of years but if they spend the time and develop some good prospects and once those prospects reach peak level to play in the majors, then they can tweak the lineup and add some big name free agents and some key trades. I think this adds a great team and possibly a team that will win for example 2 championships in 5 year period. what do you think?