The importance of the safety position is difficult to assess.  There are only a handful of impact players so the market value for an average player can be somewhat inflated for the on-the-field results.  Non-impact players populate the highest paid list (Ken Hamlin, Chris Hope, Madieu Williams).  Even with that salary bloat, the franchise/transition tenders are relatively low - only the TE and P/K positions are lower.

The draft is therefore a decent way to get good value.  You can use a 2nd or 3rd round pick and have one of the best prospects at that position without having to overpay for potential.

This begs the question: who to draft?  With only a few exceptions, the impact safeties are all ranked in the top 100.  The most notable exceptions to this have been Chris Horton and Cody Grimm.  From a workout perspective, all prospects ranked in the top 100 had a 40-time of 4.55 or less.  The exceptions to this include Jairus Byrd (4.68), Michael Hamlin (4.61).  The 20 yard shuttle time is perhaps equally important as a metric for safeties as they need to be able to change directions quickly.  Most prospects have a shuttle time of 4.30 or less.

Here is the recent draft history at the safety position.  The prospect rank / draft position is shown in parentheses followed by games played / started.

2010:

SS T.J. Ward (109/38) - 16/16, 123 tackles, 2 INT, 12 PDef, 0 sacks

SS Eric Berry (4/5) - 16/16, 92 tackles, 4 INT, 13 PDef, 2 sacks

FS Earl Thomas (14/14) - 16/16, 76 tackles, 5 INT, 12 PDef, 0 sacks

FS Cody Grimm (245/210) - 11/9, 57 tackles, 2 INT, 4 PDef, 0 sacks

FS Nate Allen (45/37) - 13/13, 48 tackles, 3 INT, 11 PDef, 2 sacks

FS Taylor Mays Southern California (31/37)

FS Morgan Burnett Georgia Tech (50/76)

SS Chad Jones LSU (74/76)

FS Major Wright Florida (94/75)

2009:

FS Louis Delmas (40/33) - 15/15, 94 tackles, 2 INT, 10 PDef, 1 sack

FS Jairus Byrd (53/42) - 14/11, 45 tackles, 9 INT, 20 PDef, 0 sacks

SS Pat Chung (49/34) - 16/1, 37 tackles, 1 INT, 2 PDef, 2 sacks

SS Al Afalava (276/190) - 13/13, 53 tackles, 0 INT, 0 PDef, 2 sacks (cut after rookie year)

FS William Moore Missouri (50/55)

FS Rashad Johnson Alabama (59/95)

FS Chip Vaughn Wake Forest (75/115)

SS Michael Hamlin Clemson (83/116)

FS Darcel McBath Texas Tech (97/48)

2008:

SS Chris Horton (339/249) - 14/10, 76 tackles, 3 INT, 8 PDef, 1 sack

FS Kenny Phillips (28/31) - 16/3, 67 tackles, 1 INT, 6 PDef, 0 sacks

FS Charles Godfrey (67/67) - 16/16, 61 tackles, 1 INT, 6 PDef, 1 sack

FS Tyrell Johnson (40/43) - 16/7, 31 tackles, 1 INT, 3 PDef,

FS DaJuan Morgan North Carolina State (53/82)

FS Thomas DeCoud California (96/98)

SS Tom Zbikowski Notre Dame (101/86)

Here's the prospect list for 2011:

FS Rahim Moore UCLA (49/?)

FS Quinton Carter Oklahoma (73/?)

FS Marcus Gilchrist Clemson (93/?)

SS Tyler Sash Iowa (101/?)

SS DeAndre McDaniel Clemson (102/?)

FS Jaiquawn Jarrett Temple (107/?)

FS Robert Sands West Virginia (118/?)

Interestingly, only Marcus Gilchrist passes the "workout metric test" although Moore and Carter have excellent shuttle times.  Robert Sands has an intriguing size/quickness ratio.