You aren't just giving up your 2nd best pick though. You're giving up your second best pick, AND full market salary price. Why do that when you can just sign a FA from a similar tier for just the money? If draft picks could be traded, they'd look for excess value. Just like any other trade, less excess value equals less trade return. So, no, I don't believe teams would trade their 2nd best pick for a player with no excess value, if they were allowed to.