From my, uhum, limited experience of a 150 basses or so which I continuously keep alongside each other in the same two environments (my office, fully air-conditioned, and my home, not air-conditioned) and as a trussrod adjustment obsessive
I venture forth the following bold statement: Once a neck is older than ten years (the occasional rubber neck candidate excepted), it needs less adjustment than when it is "fresh". That is not to say that younger necks are worse, they just breathe with the climate more, new Gibsons are especially notorious that way, going back an forth the first few years. It's not an issue as long as the trussrod works easily both ways. It does become one when the trussrod is less than willing or less than accessible. On my basses thirty years older and more I only adjust necks - if at all - every couple of years (and not always tighter either). When those basses were young I would have probably felt compelled to adjust them more often too, I'm not saying that the wood was better then, just that it is older today just as today's wood will be three decades from now too.
I used to think that older wood lost the ability to absorb and lose humidity more than younger wood, but Dave, that old owl of scientific certainty, will no doubt immerdiately pounce on me for that, where is my helmet ...