Uh.. Port and polish also brings negligible gains for lower bhp
engines... You're only removing some slight imperfections inherent
from casting techniques used to forge the cylinder heads.
We're talking a couple of % only.. So for a 100bhp car, you're
going to only squeeze about 2 to 5 bhp. Maybe something higher like
a 300bhp engine, then maybe you could squeeze 6 to 15 bhp
more.
Considering the costs associated, you could prob get better
bang-for-buck with the grounding system. 
Just my 2 cents.
