I had an idea for experience too, and figured I'd put it here rather than a whole new thread.
Right now, I think the experience through practice method for weapons is great, as well as the experience for completing quests.
What I would like to see is extending the experience through practice to other things, especially trade. Buying the correct items where they are produced and then selling them at the correct town for a profitable route could possibly result in some experience as well - you did have to execute a succesful trade route, plus, if it were a quests given to you by a merchant, you would have received experience points for it.