From a long term perspective, what did he gain from all of the oppression and over centralization of power other than fostering rebellion and instability? Once he was chancellor he could have dialed back the overt machinations continued to exist in the shadows to weaken the Jedi and grow his own power.

Hell, he could have become a sympathetic father figure to the Republic after Order 66 had he just remained as Supreme Chancellor, or even put himself in a position where he could step back and install a puppet successor and maintain the illusion of democracy while controlling the levers of government. Why create an unstable power base for himself when it seemed like he was mainly interested in doing SIth magic stuff in seclusion? Was he just bored?