Expert level will come fast enuf. I say go for a new room. Expert level is not fun really, it's harder. more items to find in less time. No big deal. No going back. Sometimes I wish I had an easier level. Just my 2 cents.
I am only at level 30, and current quests are concerned with getting into the Laboratory, for which I don't have many items to assemble the drill. These items (eg. Hand Drill) don't seem to drop anywhere either..... maybe I'm just not ready for 501 or Sakura - just eager to get my hands on some of their drop items for my collections!