Goal is a bit different. Vector doesn't collect and persist metrics. We needed something that had as little overhead as possible so it could be deployed to all our hosts and simplify the process of analyzing those metrics.
Why not? Storage is cheap. Do you use something else to get historical visibility into metrics?
Vector is for per-instance custom drilldowns. I gave a talk last year where I showed how they both fit together: http://www.brendangregg.com/blog/2014-09-27/from-clouds-to-r...