If you're winning because you play a half-decent solid game, and not because the opponents are very poor and don't care, you should be okay playing entry-level SNGs. You may not win much, but you won't lose a lot either. As you get emotionally comfortable playing buyins, you can think about expanding your game.

OTOH, if you get your ass handed to you over a reasonable sample size, you'll know your game needs work. And if you don't start feeling less discomfort, you'll know playing for play chips is where you still belong.