Terra Tower is a city?? I was just glancing at the compendium article and it looks like it's more of a religious house of the dragon God.
The switches not being touched.........The best reason would be relying on the player to give us a break here. Same reason Ganondorf leaves the exact number of keys for Link to get to the top of the tower, or the same reason an empty treasure chests sits in the same spot for 400 years if you grab it in 600 AD......
However I have thought up an answer to this question the switch that Marle hits is unreachable after Marle's finished (I'm going to put debris in front of the door. We could say that the battle between Reptites and.......humans (this may have to change), was so intense that the door got covered. The second interaction (Marle pushing rocks).....well why would they get rid of the rocks taht covered up that hole?
The third interactoin (Crono/Magus/Glenn) press that switch. It closes their door and opens the other door. THis makes the switch that they hit impossible to get to so noone else COULD have pressed it.
Finally the 4th interaction (Crono/Magus/Glenn fight a monster that drops a key to the secret boss)....well noone was looking for the key?
--jp
