For what it is worth, over his MLB career, Francisco Cordero has 177 saves in 223 chances, a 79% save rate, with a 3.29 ERA. We will be paying him $11.5 million per year for the next four years.
David Weathers in 2007 saved 33 of 39 games, an 85% save rate, with a 3.59 ERA. Weathers 2007 Salary was only $2,250,000.
That's quite a bit unfair -- comparing Cordero's whole career to a single season from Weathers. Compare their 2007 numbers and you get an entirely different picture.
And the A's model hinged on dipping into their considerable minor-league talent to acquire impact bullpen arms. That surplus of minor-league talent is in short supply in Cincinnati.
While I agree that spending too much money on a single player is risky, I think you're glossing over the specifics of this situation. The Reds' bullpen is a gaping wound, and the team isn't particularly overloaded with enough talent to acquire an impact arm without damaging the roster. They do have cash, however, and cash is much more replaceable than talent.
Spending money on Cordero doesn't prevent the Reds from going out and finding more impact arms for the bullpen (which they still need to do). It also allows the team to shop whatever surplus talent they do have for a mid-rotation starter.
This is a risky move on the Reds' part, but I think it's a measured risk that absolutely needed to be taken.