His expected batting average up through this point is .264 (based on his lifetime average on balls in play, his home runs and his strikeouts). He's a career .255 hitter. Unless you need a .255-.260 hitter with 20-25 home run power and 3b/of eligibility then it is time to give up on Casey Blake. Obviously those numbers can be useful in certain leagues (especially a deeper mixed or AL only league) but for your typical 12 team mixed league he's FA fodder at this point.
Hope springs eternal
grows like ivy on the vine
then dies in the fall
--Haiku for a Cubs Fan, The Loveable Losers