I like to keep track of large contracts and see how they worked out. I would have to say that most of them have not.
There are 19 total contracts over $100M whose terms have finished. Here's how I rate them (age at first year of contract in parentheses):
Good (5) - Pujols (non-FA, Cards) (24), Jeter (non-FA) (27) , Cabrera (first Tigers contract, non-FA) (25), Manny (29), A-Rod (first FA contract) (25)
OK -(4) Helton (29), Cliff Lee (31), Beltran (28), Sabathia (first FA contract) (28)
Bad (10) - Dice-K (I included him because the posting fee pushed the Red Sox cost over $100M) (26), Zito (29), Giambi (31), Kevin Brown (34), Johan Santana (29), Griffey (31), Carlos Lee (31), Alfonso Soriano (31), Vernon Wells (29), Mike Hampton (28)
One could argue about where I placed a few of these, but overall, the record is not good. Three of the five I rated good were not even free agent contracts. The age distribution is not surprising, nor is the lack of good contracts to pitchers.
Of the contracts that are not finished but are at least halfway completed, I rate them as follows:
So far so good (2) - Hamels (29), Greinke (though he opted out) (29)
OK (6) - Tulo (26), Matt Holliday (30), Adrian Gonzalez (not sure what to think about that--the Sox traded him quickly, but then won the World Series--meanwhile, the Dodgers haven't gone very far with him) (30), Mauer (28), Teixeira (29), Werth (32)
Bad (9) - A-Rod after opt out (32), Jose Reyes (29), Fielder (28), Matt Cain (27), Josh Hamilton (32), Matt Kemp (27), Sabathia after opt out (31), Carl Crawford (29), and you know who (32).
Still not a good record for these contracts. More than half were bad. Overall, signing a hitter who is not yet 29 is not a bad bet. Anything else usually ranges from bad to awful.
Apologies for any errors I made.