I'm becoming less and less married to the concept that Palpatine has to literally declare himself Emperor in the last prequel. Of all the various things in ROTS that bug me, the inexplicable need to explain every single thing to set up A New Hope is really up there. I think you can do more by sheer implication when Palpatine announces himself Chancellor (or President) for life than having him change whole scope of the Republic overnight. The reactions of people like Bail Organa alone will tip off audiences about how damning the whole scenario is, especially after the Jedi have been wiped out.

It adds almost a chilling element to see Palpatine making promises about how the democracy and the senate will last forever, then in the next film you immediately learn the Republic is gone, an Emperor rules over the Empire, and within 30 minutes even the Senate is finally dissolved. The audience's imagination can do a much better job of filling in that gap and envisioning how Palpatine gradually stripped away elements of the Republic until the Empire is in its place. Its more realistic in that sense and it adds to the creepy aura surrounding the Emperor; without ever actually seeing the literal events you know how dangerous and cunning this man is.