im(h)o, i don't think there'd be any benefit to polishing anything, there's just not enough throughput to make a difference, and modifying the stock pipe (too much) could possibly reduce engine life, as backpressure is an important factor. i'd suggest keeping a top-end rebuild kit handy if you're gonna get too extreme.
as a former owner of several kawasaki 3-cylinder rocketsleds, i'll be holding out for an expansion chamber exhaust...i think i saw one listed on one of the chinese wholesaler sites, so i'll wait for someone to get one and report on it.
has anyone been able to compare performance between the old and new carb by any chance? can these things be re-jetted?