If you heard from an instructor that a maintenance shutdown will divert a class from a prototype, it is probably true. If you heard it from a student: ask an instructor. They might not know, but they can ask (and they will if you ask them). The truth is, the proto-pals are OLD. The MTSs in SC were both commissioned in the early 1960's, and the NY prototypes aren't exactly new either. The only way they can continue to serve as living history museums/baby nuke playsets is through scheduled maintenance periods.
Don't worry about not going to New York. The Charleston, SC area has a LOT to offer (remember, the first shots of the Civil War were fired right out in Charleston Harbor at Ft. Sumter). The downtown area has phenomenal restaurants (strongly recommend Charleston Grill, Grill 225 and Magnolia's) and some decent bars if that's what creams your twinkie. Daytona beach is a few hours away, as well as Jacksonville (I went there for a Denver Broncos game, and it was the most polite sports community I've ever seen -- not a bad stadium either). Myrtle Beach is just up the road (and super cheap in the off season). Tampa, FL isn't too far away, either (and Busch Gardens is free for military). Those are great places to go on your four-day weekends. You also won't have to worry about Northeastern snow storms (after two winters in Portsmouth, NH, I would be happy never seeing a Northern winter again).
It doesn't really matter where you go for prototype, since you will get a decent education from it (if you work for it). If you work hard you will have a good time in SC or NY; and if you fall behind it won't matter where you live.