Sometimes tops pull and necks warp, and frets get worn, but more often than not, people sell perfectly good guitars for less than new ones would cost. I like to let younger guys do that, so I buy older instruments. The danger of this is that the playablity, and intonation of modern guitars vastly surpasses what guitars could do even 20 years ago. You don't see many really serious guitar players playing vintage instruments. Most of us get better results from new, sleek, well-made modern guitars.
Guitars sound better with age.
This also means that guitar makers who make new guitars sound too good may do so by making them too fragile for road use. A company that has been around for a long time and has made many thousands of instruments shipped to all climates will have modified their constuction techniques accordingly, and you will be more likely to get an instrument that holds up well over time. If you find an instrument made by one of those companies that really sounds great, then you may have found what you want, since you can be sure that it will improve with age, and that the warranty will protect you if something goes wrong. If you don't travel much or abuse your guitar, you can buy one from an individual builder who can make an instrument that sounds unbelievably good, but might be fragile or have a dangerously thin top or braces. Which brings us to the last point.