It's good to play gambling with sign up bonuses, but I don't think I can sustain long with it without losses. You need to experience failure first in gambling in order to win at the first place. By the time you'll be mature enough through experience, gambling management is your own way to become lucky to win the betting games.
Guess what you mean here is that getting and using such bonus is a one time opportunity on single gambling website and the chances of winning from the bonus is very low? How about moving from site to site and playing only with bonuses? That could get a gambler few wins you know?