OK, so first off while i agree a build up to the puppet master would be cool, as already stated, its to late. ESB has revealed The Emperor and so leaving the main villain till the last 20 minuets (don’t quote me on that) would be pointless,
Second the early scenes of The Emperor, specifically his arrival on the DS2, are very important in setting up the differences between Vader and The Emperor. When Vader arrives he is greeted by a force of about 30-40 troops however, when The Emperor arrives they are in a massive hanger with hundreds of troops. These really serve to show how vain and politically powerful The Emperor appears, as with any tyrant his power comes mostly from his followers (although his is shockingly good when it comes to the force) and it sets up his death to come so easily once he is betrayed by his most loyal subject.
Oh and sorry for the “Joke” i just couldn’t resist.