In the Revenge of the Sith novelization by Matthew Stover, we get a really cool bit of inner monologue from Palpatine when Yoda shows up in his office (just after the transmission with Anakin Skywalker on Mustafar after eliminating the Separatists during order 66). He says this:
"But his physical presence was an illusion; the truth of him could be seen only in the Force. In the Force, he was a fountain of light. “Pity your new disciple I do; so lately an apprentice, so soon without a Master.” “Why, Master Yoda, what a delightful surprise! Welcome!” The voice of the shadow hummed with anticipation. “Let me be the first to wish you Happy Empire Day!” “Find it happy, you will not. Nor will the murderer you call Vader.” “Ah.” The shadow stepped closer to the light. “So that is the threat I felt. Who is it, if I may ask? Who have you sent to kill him?” “Enough it is that you know your own destroyer.”
I think this is really enlightening (pun intended) as to how Sidious viewed Yoda, that he was a fountain of light itself. Renewed energy constantly flowing in the light side of the force. 
Does this give a little credit as to why he's so obsessed with Grogu, or rather, why the remnants of the Empire are so obsessed with the the experiments done on Grogu? 
Could Grogu be more than just a body to clone or transfer essence into? Could it be to, dare I say, find a means of prolonging life as Yoda's ageing process is much better than Palpatine's. 
Imagine if Palpatine lived to be 900 years old. The things he could achieve would be extraordinary to say the least.
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