Two more bits:
Regarding upgrading the Enterprise and then having her become a training ship not a decade later: In today's Navy, they have what's called a "Service Life Extension Program" applied to many of their warships to do just that. For example, in the 80s the USN performed a SLEP on the Forrestal-class carriers to extend their lives another 10-15 years (The Forrestals were originally designed for about 30 years). The process itself took a good 2-3 years per ship to upgrade electronics, catapults, weapons systems, etc. A lot of effort for only a decade or so more life. Even today a Nimitz carrier can be laid up for up over a year between deployments while they scrape the barnacles off the hull and apply new paint, however those ships are expected to last 50+ years with that sort of maintenance.
And about that launcher room - it's a good observation that the room itself is not necessarily manual at all - the only actual activities performed there involved taking the grates off, and then one cadet standing there while the torpedo made its own way down the track. It's still a little weird that they waited THAT LONG in an obvious combat situation to load the torpedo bays, though.