That of course brings in the risk that he won't be available. A very important and intriguing aspect of draft planning. What team is there that might take the guy we want and when?
I can see the value in trading back to take a guy especially now that I think there will be more trades as teams won't be as hesitant to move up into the higher levels and the huge dollars that formerly accompanied them to get a guy they really want.
This is a really good situation for teams with higher draft picks. They can try to trade out and if they don't get the offer they feel is right can simply take the guy they were targeting without breaking the bank.
I don't think that you can do this. Otherwise you end up with Calvin Pace and Bryant Johnson when you expect to get Jerome McDougle. I think that you look at your draft board at #13 and see eight guys that you'd be happy to pick, but no one with a pressing argument is above the others.
Then you trade down seven picks, knowing that you're going to get one of the guys that you really want, but also knowing that you pick up a--say--third-round pick in the process.
You can't say, "Well, we're going to trade down from 13 to 22 and get Cordy Glenn" when you know that some team could easily trade to 20 knowing that you have a gaping need (I think this is why the Cards chose Levi Brown #5 overall--because they had a dire need for an LT and couldn't get a deal that would keep them close enough not to have to choose Joe Staley also too high).
I get the allure of trading down, and the allure of trading up, but you can't fall in love with a guy and say, "Only if we find ourselves at 16 overall." If he's a guy you love at 16th overall but not three spots before, then you don't love him THAT much.