Thanks! It could have been a one off but I think Dimensional Portal is the real problem. It's ability to keep you from descending is what allows the other powerful spells to be abused. Being able to cast Improve or Gain Knowledge a few times after you've completed a level isn't game breaking as long as you're consistently going down. The problem is by consistently using portals, tunnels & ladders it's very easy to not descend and you can cast those powerful spells hundreds of times.
I wonder if increasing the % chance of going down a level when using Portal (that % seems really low) would be the easiest tweak?