1) Rosewood looks a lot nicer than bamboo... Promo images could suggest otherwise but the newest "version" of rosewood is BEAUTIFUL. All the images of bamboo I have seen so far were "ok", at best...
2) Bamboo is only about 25 g lighter... If you can feel the difference, it's most probably placebo.
3) Rosewood is more exclusive than bamboo (more limited, longer waiting time etc.) so if you want to be clever, get rosewood version ,-)
How good something looks is entirely subjective, heck even the guy you are replying to seems to prefer the looks of the composite bamboo more.
And 25g is A BIG DEAL, especially with 500g+ planar headphones. The neck muscles/tendons will appreciate the lessened weight a lot over time, if the headphones are gonna be used for years. The difference between my HE400 and HE500 in weight might be a bit more (~60g I think), but that difference might as well be 200g because that's how my neck feels swapping from one headphone to the other. So 25g decrease in mass will be a very welcoming thing too.
Won't disagree about exclusivity...although I bet most LCD2s sold are rosewood so, in the second-hand market bamboo is probably more exclusive, heh.