I can maybe take time and do something like that when I get time! Off the top of my head though, dreamlands is pretty simple. They all do decent physical damage with auto attacks, sss'haa is a LOT of physical, kaalut is poison with some fire / physical, othuyeg and ryujin are massively magic. In end-game content, I would pretty much consider it safe to say max DR % is completely necessary.
Yeah someone should do a guide in the wiki on boss attacks with information on damage type at the very least. I could do some of it but I am not as knowledgeable as some of the other people here. A server-specific bestiary guide might be cool as well similar to that found on the Arreat Summit.
I would love to try and get something like that up...I feel like the wiki is missing a lot of the technical stuff...a lot of the end game content there, but not specifics.