Amplitude here - Most of our dashboards are powered separately from Redshift. We offer Redshift access as a way for our customers to answer more complex questions not offered by the dashboards.
Why not power your dashboards with it? What do you use?
I am considering using a columnar data store (maybe redshift) with a BI tool like bimeanalytics.com specifically to do dashboards.
My guess is latency - using Redshift for short lived, small queries might not be the best.