I think there is a balance.
I worked with both local and nationwide dealers and ended up with a factory order from my local dealer at a price I found competitive.
My trailer has had a significant number of problems that were covered under warranty requiring multiple trips to the dealer over two years. Some of these have required some hard work on the dealer's part interacting with Jackson Center and Dometic. While my local dealer's service department is not perfect, they have in several cases gone the extra mile in working on difficult problems and accommodating my schedule and situation.
I could easily have ended up making a trip to Jackson Center for one of the repairs if the dealer had been less willing to carry the freight.
By all means consider the nationwide dealers. They do a great job at what they do. The case for working with them is especially strong if you aren't satisfied with your local dealer, or don't have a local dealer, or live close to Jackson Center, or travel extensively so that the idea of a local dealer doesn't really apply.
The experience of Airforums members seems to have been that nearly all Airstream trailers develop problems of some kind that are covered by warranty (either the Airstream warranty or the warranty on individual components), if used and camped in regularly over the first two years.