although I agree those who want Goku in Smash are fools, Dragonball Z is not overrated. It's impossible to state what DBZ is now in comparison to its importance to the late 90s and early 2000s. Dragonball Z was such a huge force that it basically brought an entire culture to the United States (and virtually every other country it played). Although there were anime that came before it that met with success (Sailor Moon, Speed Racer), and others that contributed to that success (Gundam), DBZ is the starting point for the anime craze in the United States. That type of broad cross cultural appeal is basically the stuff of legends.
In rewatching the series, and it superior predecessor Dragonball, with that type of context , its easy to see its greatness. remove the context would be like removing the context to an NES classic like Castlevania, and saying, well this game sucks compared to the games of today.