Star Trek never rehashed their own stories before now (actually even '09 isn't a rehash, but STID clearly is).
Yeah ... no.
TMP was blatant in its 'rehashing' of "The Changeling." "The Naked Now" ripped off "The Naked Time." The one with Pulaski's rapid aging is too reminiscent of "The Deadly Years" to be a coincidence. And so on, and so on ...
It's been said that there are only so many stories to be told. Eventually any franchise is bound to revisit one of its own.
I'll give you "The Naked Time/The Naked Now", that was pretty bad, but there is a lot in TMP that is nowhere to be found in "The Changeling" - Spock's seeking Kolinahr, Kirk's dealing with his age and the change in the Enterprise (much better explored in TWOK, but started here).
Pulaski's rapid aging was caused by experimentation with genetic manipulation, whereas "The Deadly Years" was an alien virus, if I remember correctly. Just because both stories resulted in rapid aging doesn't make it a rehash.