I can't really speak from experience b/c I can't get my hands on a vintage piece. The only thing I can say however is that w/ the current pieces I do have in my collection, they seem to hold up rather well in both perfect and inclement weather. I store them in their dustbags and when I bring them out, they're good as new. I think it also has to do w/ the owner and how they treat their bags when they're in use and if they have to endure a lot of wear and tear. I personally baby my bags so that I won't have to trade them in for a newer model. Ha! But I think LV still makes quality items. I actually prefer the canvas on the inside better than the leather but that's just my humble opinion!
I had a few LV's years ago - not knowing any better I sold them for a song and moved on - I have one now I haven't given it a run for it's money yet - but I venture to say that LV made a great bag, makes a great bag and will always be a premier, top quality, luxury bag to own and cherish and leave to daughters and granddaughters in years to come.
The quality of louis has definately gone down. With the high demand of their purses, its easy to see why. Most of my older purses are all made in france, but they are starting to make their purses in spain, usa, etc. Also, if you look at the materials of the acutal product, for example, the locks on some of the purses are all much lighter than the older ones and they look rusted sooner (oxidization) They really skimp on their stitching and some of the stitching is even crooked. SO if you were to buy a new LV, make sure you check it thorougly. I have definatly strayed away from adding new pieces to my collection. The prices and quality you get just doesnt match up anymore.