I think IE/Maiden would be pretty great, yeah. I love enough of IE's material to get tons of enjoyment out of it and they don't put much into their "performance" so I can save energy for Maiden.
However, I can't imagine there are tons of IE fans who are not already Maiden fans, so bringing them out on tour doesn't really make much sense (i.e. you aren't exposing anyone to anything new). Granted, Maiden doesn't need an opening act anywhere, so I guess it doesn't really matter.