Incorrect. You can visit your own town, but there are certain circumstances.
Every so often, when you go to update, even if you have been updating regularly, Luna may, seemingly, randomly decide to give you a new DA(and skip paying you the 5k bells). There may or may not be a way to induce this as whatever conditions it requires may only be known by Nintendo.
When this occurs, your old DA will still exist, except that it will no longer count as "your dream town" and you can visit it in a dream as if it was someone else's town, at the expense of never being able to update it again.