Yeah you could probably get a 1st, 3rd and late round pick. Or maybe a 1st and a 2nd. But I don't think that means you necessarily get 2 stud defensive players out of it. I think you have a good shot of getting decent players, but it's not a slam dunk.
Even FA is not a slam dunk, but at least it's not a crap shoot. I think you could legitimately get 2 good to great defensive players on defense in FA for the money you'd save on Dez.
But that's all before you get back to replacing Dez. Obviously you don't want to spend money in FA for a WR because you just let one go. Or at least BIG money.
Or do you want to spend one of those picks you got on finding a talented receiver in the draft?
I agree in principle. You want more draft picks and more guys playing for less money. You don't want a handful of guys taking up a good chunk of your salary cap (although I believe the Giants were able to succeed under this model in 2011). Trading Dez would help with that tremendously. But does it mean you get a return on your investment?
That's why some are saying, "When you have a special player, don't let him get away". Obviously within reason.