The JuCo route won't go well if you can't develop the young players in the mean time. However, assuming you trust Kill's ability to develop players, it really comes down to the ability to develop players, if you can't do it, whether or not you have JuCo players, you will never be decent.
However, lets assume we bring in 3 JuCo DBs...in 2 seasons, our defensive backfield will actually have some nice upperclassmen depth (Montgomery, Wells, Levine, Murray, Moss, Wells, Thompson).
We need to keep in mind that our secondary is SO thin, that we could add 3 DBs and still have a ton of PT to go around for our non-RSing young DBs.
As far as the drop off after Brew's year #3...I think a lot of that had to do with his inability to develop players...
-Michael Carter wasn't able to step up and take over for Simmons/Sherels.
-Royston got hurt.
-Dandridge got kicked off the team, he likely would have pushed Theret for a spot. If not, he would have added depth
Our problem with our defense in 2010 (after the JuCo kids were gone) was that because of attrition and other issues, we were forced to play 2 true freshman all the time (Manuel and Vereen).