There's not much you can do about carbon buildup in exhaust manifolds....it's really just a fact of life. Now if you were building a single event race engine then yeah why not...but on any street vehicle it's really just splitting hairs. The effort and money is better spent on head breathing.
There is an additional point to make. The gases in an intake manifold are moving at a much lower velocity than those in the exhaust manifold. So maintaining laminar flow is more important than in the exhaust manifold. The gases in the exhaust manifold are subject to much different flow parameters.
"The 300ZX Turbo is a dance; it's a song; it's rolling, roaring automotive art. There is no color that doesn't suit it. There is no mood-lifting chemical substance it can't replace." - Automobile Magazine
