I think adding small side quests for each world. The use of NPC(non player characters) such as the teachers, trees, and other students (I.E. Penny Dreadfull).
Use Penny as an evolving student wizard such as yourself and at the end each worlds main line quests she makes a call to you, or she appears in the common area of each world.
I personally would like to see older characters return for a new role in future areas. Perhaps Malistaire, having realized the error of his ways, could offer the player assistance in the climactic final battle of the Morganthe arc? Or maybe we could hear more from Sherlock Bones (perhaps finally get into Barkingham Palace), or figure out what's up with the unused NPC in the Great Spyre.
Penny Dreadfull was an intersting NPC that would have been fun to see used more and elaborated upon.
Some more character development within side quests would be great. More meaningful, deeper character development that can grow as you progress through the spiral worlds. Learning more about the characters (bit by bit) so you grow an attachment to them.
There could be a couple side characters that you could choose to assist and learn about. Adding some elements of choice would make the experience a bit deeper too. (ie: choices you make have an impact on the NPC's story outcome - or at least an illusion that your choice has an impact.)
Currently I do not feel any attachment to any NPCs, including Merle Ambrose. I kinda felt sorry for Malistar's wife, but that was quite brief. My strongetst attachment is to my pet hound!
