The secondary is the least of our concerns.
I know everyone is loving Hollis Thomas, and the effort from Young, but I still think we need a premier player at the defensive tackle position.
It all starts up front on defense. The Patriots have always had marginal talent in the back 7, but always have stellar defenses because of studs like Seymour, Wilfork, Warren, etc. Look at their secondary. They have an aging, slow Rodney Harrison, and nobody else. Freddy and McKenzie are fine. We could use some depth, because Craft is god awful. Harper and Bullocks were and will continue to be one of the best young safety tandems in the league.
Simoneaux and Shanle have played admirably and with much heart, but they are still mediocre at best. They look good to many of us because even they are an upgrade from what we had, but our linebackers are still below average. Fujita is the only one I am really comfortable with. We could definitely use upgrades at MLB and WLB. One of the most important positions on the field, with regards to creating big plays and turnovers, is the WLB spot (see: Derrick Brooks). I don't think Shanle has one forced or recovered turnover this year. We could use a playmaking WLB in a major way.
In summary: DT, WLB, MLB... in whatever order our staff feels is correct.