They are definitely not universally overvalued yet, but they certainly can be.
I think you look at Santana and realize that too many players sign contracts that make them enormous negative assets (I don't see how Pujols, even if he's MVP quality for the next 5 years, ever becomes a positive trade asset, which is different than thinking there wouldn't be a GM willing to give good assets for him to be clear) so if someone gives you prospects for the right to sign that player, the prospects have to win, since they can't cost enough to be net negatives.
There haven't been that many trades where the prospects were wildly overvalued, that I can think of anyway. Halladay was never fair return, but in cases like that the team is forced to a decision and it's just the best you can get, not what he's actually worth. There are many cases like that, but the GM trading the vet in those situations never believes the prospects are worth the player, only that he can't get anymore because of contract situations and the player's publicly expressed desires.
Trades like Santos/Molina, or Beltran/Wheeler where it's single player for single prospect aren't that common either, but as those two show I don't think you can say prospects are universally overvalued by GMs, although they surely are by the knowledgeable fans. These kinds of deals are simply too dependent upon a single GMs evaluation of a player to read too much into prospect valuation as a whole. If Williams is confident Molina gives him a great chance of 6 years above average 200 IP, then of course he's worth any reliever, but AA sees a piece he has to get that's going to cost him 30-40 million on the open market and gives up a single AA prospect at a position he has at least 5 players with as much upside and keeps his cheques for somewhere else (hopefully
). I think from AA's perspective Molina was overvalued, but Kenny can't win know so what are 70 IP worth at the end of games now? So much of trade value for players is situational for GMs and just because you take inferior prospects for MLB quality players doesn't necessarily mean they're overvalued. That does mean it's a fantastic way to add veteran pieces if you're looking to improve, you just have to find the places where the player isn't really worth anything to the other GM anymore and the rest of the league hasn't figured that out yet.
*Schad, if you still wanna re-roll skyrim, you should do this:
http://www.youtube.com/watch?v=uhBiNx74 ... _embedded#
