i think the tower of master is really lacking in flavor. even if it does not get a story, id like it to t least hvae a more fun mechanic. something llike this might be fun:
add a slew of new mana producing buildings. some of these should overlap and they should be spread amongst many tech lines.
also existing wonders could be changed:
also the required mana would be set to four, so when all 21 manas come out you have 5 on each and one on the tower of mastery
give the individual towers large bonii
make the towers require arcane lore
add a "super mage" hero for each tower buildable only in thata city
as soon as someone builds all four towers, a barbarian magic avatar is released on the world. this happens each time anyone buids all four towers, it should have 0 strength chanelling 1 to three, sorcecry, sommoning, twincast, melee unit, afinnity 1 for every mana. when it is defeated, the unit gets a " magic essence" promotion. when brought to a city you can remove the promotion and put a magic essence building in the city, that gives 5 exp to arcane units built in the city, and allows the civ to build the tower of mastery. if the civ that places it in theircity does not have all four towers, then a new magic avatar is spawned that will not attack a civ with the magic essence building.