Thanks a lot for the responses!
Yes, I remember, the menu disco, hardly a secret, but the ball is needed to get there, so probably that is it.
Concerning the race: That's what I suspected, thanks for the confirmation.
----
So the last open question is the one about screens x31y40 und x32y40. I dug a little deeper, and they are part of "Stranger Dream", the same level as the race thing. These screens contain a conversation, which according to the script files is as follows:
Do 0=(Do)Hey Sister.
Do 1=(Do)Do you remember how to travel through the disorder?
Do 2=(Do)If it's too dark, stand still for a few seconds to shine. Don't move even a bit, otherwise it won't work!
Do 3=(Do)Patience is the key; the more you wait, the longer the light will last last. Just remember to stand COMPLETELY still.
It seems to be a reminder on how to use the disorder as part of the disorder sequence in the dream level. But I cannot find out how to get to those screens to get that helpful reminder...