Dragon Ball is 30 years old and yet it still attracts new fans, still has a rabid fan base, still has calls to return, still sells well, is still SJ's most acclaimed series and despite ending in 1997, still has new movies and new games. There are very few Manga's that can boast that.
I doubt that Naruto will still have movies and games in 20 years, though I hope so
I understand that not everyone gets Dragon Ball but if all it had was nostalgia and a few fights then it would only have endured with its original fan base.
Dragon Ball is simple, he never over thought it, never filled it with blood, guts, death and unhappiness and I think that is the key. Manga's like Naruto, for all its glory and it is wonderful and Bleach and most other modern Manga are depressing. Dragon Ball is like the summer time when you are a kid, all it has to offer is excitement, enjoyment and fun. It doesn't make you feel sad, doesn't break your heart and doesn't make you dread the next attack in case your favorite character got bumped off.
All the arguing that goes on now over Naruto and Bleach and co, all the disappointments, all the dropping the story because the artist made a horrible mistake, none of that applies to Dragon ball because it is what is it. Dragon Ball took us on a journey and an adventure and it never made us feel more depressed in our already unhappy lives, it did what it was supposed to do, it took us away to a world that was not our own, one filled with humor and excitement and big characters and not to a world that was just as or more unhappy than the place we came from.
I understand that some people like stories that are filled with death and angst and drama, well maybe they have really happy lives or maybe they are just depressed and want to stay that way XD but I for one like a story that takes me away from the pain of my life and I think Dragon Ball appeals to people like that and is one of the many reasons it is appreciated by its fans.