You know, the Seymour references bring home just how hard it is to pin down the impact of a major trade, even with the benefit of hindsight. What if the Patriots hadn't traded Seymour? Let's try to figure out what would have been different...
First off, what they received was a 1st-round pick, which they used on Nate Solder, and cap savings, which is generally agreed to have gone toward re-signing Vince Wilfork to a long-term deal. If they had chosen to extend Seymour instead of Wilfork, they would have been in need of both a left tackle and a NT/DT, without the benefit of the extra first-round pick.
In that situation, could they have afforded the luxury of trading their own first (#28 overall) to New Orleans -- a trade that ultimately turned into Chandler Jones and Shane Vereen? Likely not. My bet is that the pick would have been an OT, since NT was a very weak position at that point in the draft. (3-4 DE was much stronger, but you just kept Seymour over Wilfork, remember?) Meanwhile 2 highly regarded options remained at OT in Gabe Carimi and Derek Sherrod. Both, in fact, were selected before the end of the first round..and neither lasted to the end of their rookie contracts.
So now you find yourself with Seymour but not Wilfork, Jones, or Vereen, and with an execrable starting LT. Ouch. That trade's sure looking good!
But maybe it was totally different. Maybe you didn't re-sign Seymour OR Wilfork after the season, and poured the money into FA Jordan Gross at LT. Then you hit the jackpot by drafting Muhammad Wilkerson in the 1st to replace Seymour, then up Jurrell Casey in the 3rd to replace Wilfork. Amazing! But oops, now you don't have Steven Ridley or Shane Vereen. (Or Chandler Jones later, of course.) So let's pencil in RB Jacquizz Rodgers in the 5th in place of Marcus Cannon, and...
Quick now, what was the impact of trading Richard Seymour?