Having $30m to $40m in cap space to spend on DL doesn't matter if there aren't DL worth spending it on. Unless there are off-the-field issues or they had a giant rookie contract that predated the rookie cap, top young DL rarely hit free agency without a tag.
The top 3 untagged DL FAs in 2014 (by contract value) were Michael Johnson, Lamarr Houston, and Arthur Jones
Top 3 in 2013 were Desmond Bryant, Ricky Jean Francois, and Cliff Avril
Top 3 in 2012 were Mario Williams, Mark Anderson, and Broderick Bunkley
Top 3 in 2011 were Charles Johnson (resigned), Jason Babin, and Ray Edwards
Not exactly great buys. The best one available next year is likely the guy we just added to our roster and he will probably cost a lot.
Meanwhile, setting the last two draft years aside as too early to assess, here are DL drafted around the back 1/3 of round 1...
2012 - Chandler Jones, Whitney Mercilus, Nick Perry
2011 - Phil Taylor, Cameron Jordan, Mo Wilkerson, Cameron Heyward
2010 - Dan Williams, Jared Odrick, Jerry Hughes
2009 - Peria Jerry, Ziggy Hood
I'm not just cherry picking the ones that made it. They all made it. All start or started at least some. Nearly all are regular starters and a few are pro bowl level.
I'm all for BPA. The problem is when DL has the potential to be BPA we trade up or down or tie goes to pretty much any other position, meaning it's very unlikely to ever work out to be BPA. So then we're trotting out the Haydens and Selvies of the world as starters.