If you can get a top prospect in the draft with your first pick, you take him and get him for 5 years. Gilmore was a good corner in his time here. We got good value for the pick. And while some are disappointed that he did not become "elite," all we have to do is take a look at the other names that came off the board around him and discount hindsight. It was a good pick and we got five years of, at worst, serviceable play at a difficult position. The issue comes down to money in the present. Was good CB play worth game breaker money? Absolutely not. Maybe the Patriots think he can be even better than he was here, but also maybe they have a top team already and can afford to pay whatever they want to a corner that can be sturdy of the next few years. Meanwhile, we have extended contracts at other positions for our top players (McCoy, Glenn, Incognito, Hughes, Dareus, Taylor) based on their value to our team, the market for their position at the time and certainly other factors as well.
Of course, it's also hard to compare picks over regimes especially since our team has gone through so many changes in the past couple decades. With a deep DB class in the next draft, it's possible that we have a plan!