Part of the reason they actually rescaled things is because of the light speed theory put out by Hawkings back in the early 80s.
It wasn't purely a cosmetic change, it was in part because going back to Star Trek through TNG gave TPTB the opportunity to try explain things more accurately as we understood the light speed threshold barrier theories then. Since then though, our theories have changed a lot (again).
I admit curiosity what light speed theories you mean.
There's nothing too mysterious about it; Star Trek was originally pseudo based around Einsteins theories that pushing past the speed of light required all sorts of energy we'd never be able to master (thus part of the reason the actual reactor on the original Enterprise was so huge).
TNG updated its theories to be based more in line with Hawkings theories, though it still took liberties. Hawkings only added to Einstiens theories, but of course, he was one of the major theorist playing around with dark matter the existence of multi-dimesional space.
Michu Kuko talks about both theories in his book, Physics of the Impossible. Its a must read for anyone interest in Trek tech.