In a room in the subterranean hell there is a stone ball on a seesaw thing. when you hit the opposite end, it budges a bit but goes back. Is there anyhting i can do in that room?

do you have the Mjolner yet? If not, upgrade your hammer to get that. Then go back there, hit the see saw and the ball will it 3 different bells. It will drop a potion, a high potion, and the most coveted Super Potion.
If you hit the see saw with a lesser grade hammer you only get one type of potion, and that will stop you from ever getting the other 2.

then the room is quite pointless then really

Well, not really, it's the only place you'll get a Super Potion in the whole game. I'm pretty sure that no-one drops that. The drop's are mostly potions and occassionally high potions. And the super potions refills all HP, no matter what level you are at.

Well, I know that there are more super potions in the game (I have 4), and I know that final gaurds drop them though I haven't seen them drop them before (my friend told me).

yep the final gaurds drop them and equip the rare ring and go and fight loads and you have 9 in bout 5 mind