Randalf
Ancient Mariner
Obviously, we never want a situation where the band is interacting with non-real things. There's a reason Maiden has the best stage show in metal and that's all the time to craft that goes into it.
When it comes to screens: I think there's a place for them in an Iron Maiden show, but I think the place would have to be very creative and not distracting. Not just to make up the entire backdrop, but if there was a section of the stage (mirrored, probably) that could be used creative, that might be fun.
Preciseluy! The ice element of the Maiden England show or even the stained glass of the LOTB show are elements where the clever use of screens might have worked very well, where as TBOS stage, for example, didn't need anything like that at the slightest