Given the bust rate of QBs in the draft, there probably isn't a starter in the NFL I would trade (assuming I am that QB's GM) for a rookie.
Not Geno Smith. Not E.J. Manuel.
Even with a BAD starting QB, at least I know what I have and how much insurance I have to buy to protect my team, ala signing Michael Vick as a backup. Backfired? Absolutely. Smart move? Absolutely.
Guys like Luck happen on rare occassion. Guys like RG3 and Blake Bortles happen every single year with high consistency.
I would never trade a known commodity, no matter the value of that commodity, for an unknown variable like a rookie prospect. Not under any circumstances. Not if I wanted to keep my job as a GM.
... now can someone please give me a job as an NFL GM? I'd work for a lot.. LOT... less than the other guys. We don't even have to talk seven figures. $500K would be fine by me.