Has anyone tried combining multiple spacers?  I have a half-inch four hole and a one inch open spacer, and I was considering stacking them to let the airflow smooth out a little after the butterflies before hitting the open plenum.  I wont know for sure until I try on the dyno in a few months.  

What you're speaking of is not a new concept, but is definitely worth trying on the dyno.

Wilson Manifolds - Combo Spacers  

Cool.  I didn't know they came as single-piece units.  That'd eliminate a gasket.  If it works, I might upgrade from my cheapo knockoff and get a quality spacer.