Wow. I haven't seen so much passion since Temple of Light.
Let us define 4 above-the-curve power levels here.
1. Undercosted = popular in books because of cost-benefit analysis
2. Auto-Include = compulsory in all eligible books
3. Overpowered = needs to be nerfed as it is game imbalancing
4. Broken = needs to be banned as nerfing it makes it useless
Wizard's Tower is definitely at level 2. It is under-costed, has ready marker action burst flexibility, free switching utility (only increases with more attack spells), not Zone Exclusive (easier to protect) and Unique not Epic (morale-sapping knowing another may arrive if destroyed). What were they thinking?
However the tech exists to handle it. The Warlord has Akiro's Hammer (under-rated silver bullet against Wizard control). Any Earth mage can cause a favourable mana trade with Steel Wall (before Acid Ball). Add Archer's Watchtower behind Wall and a ranged creature? Any mage can take it out with useful Grimson Deadeye. I admit the problem with burst damage (Force Hammer, Earthquake, Hurl Boulder, Thunderbolt on stick etc.) is you invest more mana (and actions) than the Tower so you come off worse. But there is tech out there even now and if it really creates problems, you need to include this tech in your books.
Because Tower is Arcane Mage Only, I just view it as part of the Wizard package, just like Galvitar is part of Forcemaster package. I read it as an unwritten ability on the Wizard card: "has access to Wizard's Tower". This access was one of the reasons why I felt a Wizard would win Gencon. Also why I was so surprised by the recent Con results (6 Beastmasters, 1 Wizard?) because Wizards are too good currently.
As someone who vocally kicked and screamed that Temple of Light needed nerfing (even more of a brat back then), there are a few key differences here:
(a) Wizard's Tower requires mana (and extra spell points) to use unlike original Temple of Light
(b) Wizard's Tower is an Arcane Mage Only benefit while Temple of Light could be in every book
The question when building a Wizard book is "1 copy or 2 of Tower?" It is bad to be a compulsory card irrespective of element or strategy. But every Forcemaster has Galvitar. Tower is just an extension ability of Arcane Mage. Those who play Magic will remember Skullclamps, an artifact that could be played in almost every deck hence became ubiquitous. It wasn't that broken but made the meta dull as it was in every deck so had to be banned. Ubiquity is not possible with Wizard's Tower. Being compulsory is not a problem if access is restricted.
Apart from Devouring Jelly, we have seen no Wizard love in the new cards so far. In fact, we have seen mechanics like Corrode to reduce resilience of Wizard's Tower, Battle Forge, Iron Golem and armoured wizard with Voltaric Shield. Also all these new conjurations means more conjuration hate like Earthquake, Force Hammer etc. Living creatures can be pumped by Etherian Lifetree so there should be more swarms and Wizard's Tower cannot cast full action zone attacks. Wizards also use equipment more (those Teleport Wands) and Orchid helps curtail this. The meta will change significantly.
I personally think Teleport and Enchantment Transfusion are far more to open to abuse than this 3 armour 7 life corporeal conjuration that needs mana to be useful. There are subtler plays than just placing Tower/Lighthouse in Near Centre, knowing that the extra resource cost to remove it gains you tempo. However, there is no doubt Wizard's Tower is very powerful, borderline overpowered - when it needs nerfing.
I think they should have written it "you may bind any number of non-Epic quick action attack spells", removing its change spell ability last line (so less text). When you cast it, you work out how flexible you want it to be, how many spell points you want to invest, while opponent knows what it can cast, does not have to worry "what if his Tower can cast X?". If this is still too good, maybe change Unique to Epic Zone Exclusive but I don't think that's necessary. The key ability is its unknown utility (which defines it, like a Wizard's versatility) and this would retain that flexibility but as a front-ended spell points investment cost, removing its unknown capabilities.
However, we are at the cusp of a major new expansion. The designers know about cards like Wizard's Tower and Battle Forge and we can assume (and see) that they have taken steps to undo these excesses of the past. So please let's just wait a little while until we get the new cards and see how the new meta settles before we call out for the nerf stick to be applied?