Exactly, Sith go on blind rampages with no real goals. They destroy because they can. To what end? They don't care. Power itself is rarely the goal of a group or an individual, power is a tool to achieve other things e.g. government, freedom, wealth, pleasure, peace etc. The Jedi don't want power, they only want peace. Most Sith just want power for powers sake. This is where they fail because if they continue to pursue power with no real goals or aims, the power will consume them, their quest will eventual end and they will be destroyed. The Emperor was paranoid, and his quest for power drove him to insanity. The quote shows he had become trapped in a perpetual cycle of a never ending quest for power which could only end one way: with his inevitable destruction.
do they really need to hold a grudge to raid them? sheer joy of combat isnt enough ? exhilirating chaos at work and undoing of those who opposed them ? both, Jedi and Sith are cultists, both indoctrinate, it is not like a Jedi who leaves academy is not bend on defeating Sith. but isnt in fact power itself the greatest goal for an individual or group? to do whatever you want, you dont need government or anything else, you simply enjoy your moments in whatever way you want, you are not bend on serving but living the life you want, how long you want.
and I think this is the best presented by this probably most known quote about Emperor:
"You discern a fraction of reality. Beyond these stars exist other galaxies, other worlds, other beings. I will experience or ignore them as I wish. I will spend eternity becoming everything: a farmer, an artist, a simple man. When the last living thing in the universe finally dies, I will enjoy peace and wait for the cycle to begin again."
she was simply corrupted, body and mind just her ways were different, most probably because she lacked power to achiev other goals.
most Sith meditate, it is not uncommon practise for them
And yes, Sith meditate. But they rely on emotions to achieve immediate power. Sith sorcery and meditation are just steps towards achieving true power, in ways other than grasping blindly for it.
And about Traya, other goals? She was the only Sith whoever had a goal that didn't involve claiming power for powers sake.