Thanks Brian. Reading through your links It seams as the reasons I expected were correct. Paella started as a "workman's lunch" dish, a cooked outside in the open with what they had. Being that the origin was in Valencia Spain ... the wood they had most readily available was ... yes ... orange tree branches (along with olive branches).
OK. So now if you want to stick with "authenticity" and such ... go ahead with the orange wood. I don't really think however, that it's got much to do with anything other than fuel for the fire. Oh yeah ... I could be for certain wrong ... but I don't think so.