Having reworked my lvl 10 Magus so he works correctly now, I noticed that the Metamagic arcana doesn't scale. I think this would be a cool way to keep the arcana evolving with the magus. For example, you can take Empowered Magic at 6th level but you can't select it twice. Why not have the option of being able to use it twice per day at 9th level instead of selecting another arcana?
Just a thought.