I get my definition from the majority of superheroes that I've seen in cartoons. Which I thought is how you define things. I could be wrong.
"Those reasons don't say they're not Superheroes. They say that they're not exactly like some other Superheroes."
Okay, if you take away the occasional planetary threat that superman fights you would still have a hero. Superman would still use his powers to fight crime as does batman and other superheroes. I know only a little bit about the fantastic four, but I gather that if you removed the planetary threat they also would use their powers to help everyday people. If it wasn't for the planetary threats or people coming after them, Goku and the others would only work out and fight in tournaments. They don't feel any obligation to use their powers to stop ordinary criminals. Saiyman is a superhero, but Gohan only gets the alter ego because he became involved in the normal human society. If he was still studying at home he wouldn't go out and save burning buildings.
"They may work only on a larger scale (protecting alien threats) but they're still doing it to protect the planet. They have powers, and most of the saiyans have at least some inborn power"
The saiyans do have some inborn power, but its nothing compared to the powers they obtain by training. Gohan had some natural abilities, but he had to train before he was actually of any real use to anyone. The only other hero like this is Batman, but again, he doesn't have any real powers.
RogueMartian, Prisoner of Circumstance
I'm gonna sleep this off like a baaad hangover
"Cuz, y'know, nothing says stealth like neon-friggin'-orange." -Conekiller