Last run through the tower, two ingredients were needed for Omeluum's potion, both of which can be found in the same room. With those, talk to Omeluum to progress that quest.
There's an interesting chest with neat boots on the balcony of the first floor you enter. (The one with the big doors, guarded by turrets.)
Reading books in the tower will reveal commands you can give to Bernard on the top floor. It's accessible by activating the elevator on the bottom floor with a sussur flower.
If you've dug up the dog's grave, its collar will "activate" somewhere in the tower. Not sure exactly where or what happens as I've never tried that.