Baserunning still plays a part for the extra base hits, but speed alone does help beating double plays and infield singles. It has merit, but not the sort to overpay for. Hermanson in $ is one I loved for his speed, but wasn't worth his price when he wanted $6m as a free agent this year. Cheap speed is easy to find, especially on a bench guy with positional versatility.
I never want to overpay or overrank a player strictly for speed. Hence my apprehensiveness in that cribsheet thread about those centerfielders.