I largely agree with what you're saying except a few tweaks. I just can't see how drafting a developmental QB makes any sense priority-wise this year. Maybe a 5th or 6th rounder but then again, what's the point in that? You can sometimes find "hidden gem" players back there for the future at OG for instance but rarely at QB (remember Enderle?). I agree, may as well just go the udfa route most of the time--the quality will be pretty much the same, which is LOW.
It's true that Philly leveraged Cobb for value in trade and so did KC with Carson Palmer. Of course neither of those franchises were able to do anything with that trade value yet. Green Bay actually got nothing for Flynn--he left in FA last year after than that one huge game he had, got big bucks to be Seattle's "starter", and then promptly lost his job in PS to Russell Wilson. Perhaps they tried to trade him and no one bit knowing he was going to be overpaid based on one game and the "GB QB" aura and the fact that he was definitely leaving in FA anyway to escape being forever buried behind Rodgers on the depth chart with little chance to ever start.
As far as offseason moves go, we definitely need to sign an LT in FA and that will be pricey no doubt. We won't be drafting high enough (top 10) to have a shot at a starting caliber rookie LT, so unless you want Webb starting again next year (who would be in favor of that?) his upgrade needs to be a FA vet. Vollmer is damn good but I believe he's a RT only and we aren't going to have the $$ to sign 2 OTs on FA. Especially if we also target a vet TE like Keller, which I'm all for if possible as long as we wrap up an LT first. Carimi is currently a stopgap at RG due to Louis' injury but he's too tall to likely ever be a permanent OG. Next year, after a full offseason to get 100% from that knee, he needs to stap it up and play RT well. That leaves us with spending a high pick (the 1st most likely) on an interior OLman and the 2nd on a LB. I agree that the 4th would be best used to find some small school speedy slot WR with hands to develop as a Knox/Hester replacement on the WR depth chart. Other teams do it all the time...so let's do it too. That's how I see it right now very preliminarily of course.

