Shields was one of the most important players on the rays during the 4 year stretch where they made the playoffs 3 times. If you think pitching 200 innings with 200 strikeouts every year for a low payroll team is overrated then you do not know baseball.
Anyhow i read up on the prospects, Myers is supposed to be a beast. Keep in mind that that the royals current big league roster is full of these bigtime prospects. Eventually you have to actually start to win in the majors, not the minors. The royals really had no way to get pitching, they haven't been as savy as Billy Beane.
Anyhow this really is only bad for the royals if Myers becomes a perennial all-star. If the royals make the playoffs or even just contend the next three years its worth it for a club that has been as bad or worse then the Pirates.