I do not know if it is cost efficient or even doing much, but what I can say is that I got one guitar (somewhat superstrat style) with ebony board and several with rosewood. The one with ebony is a maple / mahagony 5 piece neck through with swamp-ash sides and madagascar ebony top and back (both rather thick). Now this is a neck through and seriously heavy as all f*ck, but honestly the brightest of all my guitars by far. Even brighter than my Ibanez S series which is a thin piece of wood. No, this one is brighter. Also deep in the bass and not britle or anything mind you, but it has a very distinct top end and very present and bright attack. This is noticable acousticly and amplified and this baby has Crawlers in it. Still, brightest attack out of all my guitars. Makes for a cool sound having all that character, warmth and fatness from the Crawler with more bright attack than my Ibby which has a Rebel Yell.
Shame I do not like to play on the neck...makes me wanne sell it even though the sound for low to mid gain is absolutly glorious and unique.
Of course I can not say how much the top and back contribute and how much the board does, but I can surely say that ebony seems bright as heck to me.
