What value have the non-biblical Dead Sea Scrolls for the biblical scholar? The document linked below provides just one example.
While researching for a paper on Isaiah 8:11-22, I became quite captivated by a textual problem in Isaiah 8:11 (BHS 8:11 "b"). Working on this problem piqued within me an interest in the non-biblical Dead Sea Scrolls because though the quotation of Isaiah 8:11 in 4Q174 is not extant, the preceding lines are instructive as to how the author understood the phrase ויסרני. See the linked document for my explanation of how 4Q174 is relevant to our understanding of Isaiah 8:11. [UPDATE: DOC PULLED FOR A FULL REVISION] Here are a few lines of introduction to the issue:
The second half of verse 11 opens with a much disputed verbal form, וְיִסְּרֵנִי. As it is pointed in the MT, the verb should be read as a piel wəqatal from the verb יסר, “to admonish"... Nevertheless, there is support for reading סור, instead. If יִסְּרֵנִי is a piel wəqatal from יסר, the pointing is irregular... One witness that is not often brought to bear on this text critical problem is 4Q174 (4QFlorilegium)...
UPDATE 10/2012 - In the conclusion of this document I say that I think one should read a verbal form from the root סור. Shortly after posting this I changed my mind. I will soon post my updated "final report," interacting with Dominique Barthélemy's Critique textuelle de l'Ancien Testament. UPDATE 6/30/13 - The revised paper is available here.