I'm brainstormng here:
Anakin appears as a ghost at the end of ROTJ but Obi-Wan and Yoda didn't teach him that.
Palpatine appears to have multiple voices as well as multiple personalities. Perhaps he is a vessel carrying Darth Plageus and Plagues' Master as well? He doesn't seem to care about dying in his fight vs. Yoda. It's either insanity or extreme over-confidence.
Perhaps "cheating death is a power only one has achieved" refers to Plageus saving his Master (un-named) and teaching this to Palpatine. In his Sith alchemy experiments (EU fans look to Naga Sadow) he also created the perfect Sith Lord (Anakin) and always intended Anakin to rule. Palpatine offed his Master because he feared Plageus would kill him and replace him with "his creation (his son, in a manner of speaking)."
But those received would continue to rule eternally - like Plageus, etc - existing in the Force and contributing to the multiple voices of Palpatine. "A powerful Sith you will become." (It sounds like a Seer probing the future, not a current conqueror about to sieze power).
So Palpatine was not afraid to die because he would exist in Anakin along with Plageus, etc.
But the Jedi could do this as well. Qui-Gon was somehow caught in this "between life" and Yoda and Obi-Wan joined him. Anakin did as well since there was no continuation of the Sith line when Darth Vader died (we presume - or he joined with Luke - "Yoda will always be with you." etc.
So Anakin returned with the Jedi (ROTJ - get it?) and the Sith were screwed with their concocted scheme.
But it also explains "At last we will have revenge...."
I wonder if I'm onto something here but I need to take a break and re-read and reconsider this.