Are all the powers so useless? Should I even bother to fix it again?

You mean the Orrery?
I wouldn't call it useless. If you're only playing the mod for the powers, then maybe. But personally I enjoyed the quest. And I found some of the powers - particularly the one that gives +20 to Strength (=100 pounds more carrying capacity), and +20 to Intelligence (=+40 to Magicka), useful.

Meh, it was over pretty quickly but I guess the quest itself was decent. All the powers I remember getting though were a mixed bag at best. I never saw one even remotely that good.

There's a page on UESP that shows all the different powers you can get, and when. As you've probably guessed the power you get is based entirely on the moon's phase.

I adore the Orrery reward powers because they are one of the few ways to get the 'drain attribute' into your spell book. I find drain speed to be quite a priceless component on my bow and several of my spells.

http://www.uesp.net/wiki/Oblivion:Drain_Attribute

I found it rather lame as-well.. :shrug:

I only do the quest to shut Bothiel up.

I found the Orrery a brilliant expansion, it always bugged me to have that door and no way to get through it, also the interior is quite beautiful, also I love the fact that some morrowind items returned for this quest.

Since it was bundled on KotN expansion when I got it, I can say for me its a ambivalent dlc.
On the one hand its just a minor quest, with what most see as a minor reward..
On the other hand I don't rpg for rewards, its a reason to explore a part of Cyrodiil that most really would not other wise, the bandits carry a ton of items.
Acadians pointed out that all the powers effects even the bad ones have a use if you think how to use them, and Unkown Chemists said any link to past games is a nice nod to fans of the series.