This Neyer piece, which references a Dave Cameron piece, is one of many investigating how much Pujols is worth and how much his contract should/will be (and with whom).
But I fear we're asking the wrong question.
The right question is, "Can the St. Louis Cardinals get a better return on investment by spending $xxx million on Albert Pujols than on anything else over the term of the contract?"
These questions are similar, but not the same. Not at all. Even if Albjert Pujols doesn't project to win $300 million worth of games over the next 8-10 years, that doesn't mean that there's something more productive that the Cardinals can spend that amount of money on over time.
That said, assuming a $300/10 deal, is there a better way for the Cardinals to spend that much money over that period of time? If the answer is no, then they should make the deal.