Basically what it comes down to is Wizard's tower does something almost no other card in the game can do, at a ridiculously cheap price.
Lets start with it's channeling 1 trait. It's comparable with a Mana Crystal in that regard. So that accounts for 5 out of its 7 point mana cost. It's also an Elemental Wand, so that's worth another 5 mana. It also lets you prepare a different third spell each round, so that's Mordok's Tome, which is another 5 mana. But maybe we'll call it 4 since it can only be an attack. It's also an extra action, the going price of which seems to be about 5 mana or more (see spawnpoints e.g.) And finally, it's a Ready Marker Conjuration, so it can act in combo with your other actions. I don't know how much that's worth, but using the Druid's flowers as a guideline I'd guess at least 3. We'll also say that those three flower points include the cost of avoiding Zone Exclusive. I'd also want to charge at least 1 mana for the superior armor and health it boasts, compared to Mana Crystal.
To be fair, it is immobile, which is probably worth a discount of some kind since it does attack. Slow seems to be worth about -5 on an Iron golem, but maybe only -3 on Gorgon Archer. I'm comfortable saying total immobility is worth -5 points on a ranged attacker. I think I'm being pretty generous here, actually, because it's not like Mana Crystal can get up and run away when attacked, so that should be baked into the base price; but why quibble?
That puts the Frankenstein cost estimate of Wizard's Tower at approx 18. It costs 7.
Is it any wonder there's a lot of groupthink about how to play the only mage allowed to use it? It could lose both Spellbind and Channeling and still be cheaper than par.
