Conclusion;
If an NFL roster can truly be judged equally by the bottom tier players as well as the top tier ones, then it only follows that the changes of an off season can be judged by the changes in these tiers.
If that is the case, then the Dolphins may have significantly improved its roster even more than a position-by-position analysis would suggest. The team's top tiers have expanded slightly and become better diversified, while not losing overall talent. Meanwhile, the team's bottom tier has received a comprehensive lift compared to the dregs of the 2005 roster.
It would only follow that the team is in better position to absorb the injury issues that occur naturally during an NFL season. The team may also see a slight boost in special teams prowess, and on defense the team's specialty packages (nickel, dime, goal line) should see a boost in ability.