I've written about my motivation for creating Vraple on my blog: <a href="http://saltvedt.github.io/2013/08/06/searching-and-retrieving-with-vraple/" rel="nofollow">http://saltvedt.github.io/2013/08/06/searching-and-retrievin...</a>
I'd definately recommend adding in some other variety, since DDG is basically a wrapper+intelligence already. I do like the concept of the "meta search" but this sorta reminds me of Cuil...