Nothing against older bikes for a long trip. I am of the opinion that the bike you own is the greatest bike made. Then there's affordability. Older bikes can be had more cheaply.
That said, it is MY preference, not that it should be anyone else's, that newer bikes are better for me for longer trips. And I can afford them. I travel these days on a new Bonnie, which I consider the best of both worlds. A ride similar to (not exactly like) a classic with modern reliability and maintenance intervals.