[DustyPorViva]

It can work in every direction.
A server with good scripts could possibly do well without great levels or graphics. I'm sure no one plays Zodiac for its graphics or levels. Just the system it uses.
A server with good levels and simple scripts could be just as successful, it never stopped Classic or UN.
A server with good graphics may not need good levels because a good tileset can make any level look pretty. The same applies for the scripts, doesn't need anything great to be successful.

So as for what's most important, it depends on what you want. You're probably not going to get far trying to make an advanced RPG server with complex systems if you can only offer levels or graphics. On the other hand, you would probably be able to get far making a classic-type server.