I think that at one time or another just about everyone turns down a trade like the above on the Carpenter side which obviously makes sense from a value standpoint but when it comes to "names" and/or reputations, stinks on the surface.
Last year, I traded John Lackey and Morgan Ensberg for Sheets before Sheets got hurt. I thought I got a great deal, and the league grumbled like crazy that I was ripping the guy off. Well, obviously I wasn't, as Lackey produced last year and has shown this year that it wasn't a fluke. We all know what Ensberg went on to do - it turns out that "I" was the one getting ripped off.
Valverde is a PERFECT example of this phenomenon, and I'm glad you brought him up. He's gonna go for 35-40 saves and 80+ strikeouts this year with respectable ratios - that puts him at the top of the second tier of closers. But no one, and I mean no one, will every pay for him as such. I drafted him late in every league I am in, and in auction leagues where closers go for low-mid 20s, I got him for $10. I then traded him for Podsednik to an owner who is a little older and knows values vs. perception is usually wrong. The league immediately started in about how I ripped him off - meanwhile it's been as fair a trade as can be. It completely helped us both - which is what a trade is supposed to do.
I believe this is my longest post ever! Great, great thread.