Eclipse: Marm said to play safely, not that you couldn't play underbankrolled. Some people have played below their BR and done well (I've done it a time or two), but when it comes to long term stratagy and play, being within your BR is a good idea. It's also something thats a good idea to get used to. It's easier to play a little below in the penny games, but if you make it a habit, when you get higher in levels, it could really hurt.
To the OP: I play almost all Limit games (with the very few NL tournaments I've joined being my only source of NL play since I started). I have recently played a few PL ring tables and ventured in the NL ring once or twice. I can say that the stratagies and tactics are completely different and what works for limit won't work for NL.
I think Limit is more about the mathmatically correct move everytime. NL is more about reads and feeling. I am planning on playing in more tournaments this year as a way to keep poker interesting, increase my BR (hopefully) and basically because I suck at them and I don't want to suck at them anymore

. I think my foundation in limit will help me when it comes to displine and hand selection, but I know it hurts me when it comes to bluffing, making moves to win before you get to the bubble, punishing the limpers and basically just playing a good tournament.
I've also found that the few times I've had what little information on tournaments i have come together inside my head and I play well and win (or just get ITM) I have a hard time going back to limit ring. It usually takes me about 100 hands or so to remember that I can't push these people around with my stack. I don't think I would use limit as a way of improving your NL game. If you want to improve your NL game, focus on books and material designed for NL.