I owned this all-mahogany 1964 Gibson LG0 (seen here in December 1965) from 1964 until 1976 and it most assuredly opened up over that time. Wish I'd never sold it...
I have a 1996 Taylor 412-M that I bought used in 2007. It sounded pretty good when I bought it and it sounds even better now. I recently bought a Taylor 528e and a 322. Both sound amazing now...if/when they open up over the years they will sound unbelievable!
BTW, Bob Taylor says that most guitars will open up over time whether you play them or not. FWIW.