First of all I need to say - What a great mod! You've done really well at rebalancing the spells of the game. Most of the changes you've made are changes I've thought about. Most creatures who use offensive spells seem to have become a lot stronger after I've installed the mod, lukily I use Battle Extender + Experience so the extra creature hp balances out nicely.

I still feel Town Portal might be a bit overpowered and I have a suggestion:

Teleports your hero to a friendly unoccupied town.
none : Teleport to nearest town on that map level (surface or underground), needs a full day worth of movement points (like digging for the grail).
basic : Teleport to nearest town on that map level, costs 80% of heroes movement points.
adv. : Teleport to any town on that map level, costs 65% of heroes movement points.
expert : Teleport to any town, costs 50% of heroes movement points.

Alternatively if % of hero movement points is not easy to script the values could be flat numbers like - none: full day, basic: 1500, adv.: 1200, expert. : 900.