I agree that it's largely a matter of what your goals are and how you prioritize them, which can change ovre time. If you just want to have fun playing and aren't too concerned about losing a few bucks, then go ahead and play loose, bluff whenever you feel like it, etc. After all, it's just NL5, which means you can lose (or should be able to lose) a lot of buyins without seriously impacting your lifestyle.

OTOH, if beating NL5 is really important, then improving your ABC play and your categorization of opponents will certainly help. But keep in mind that if you train yourself to play nitty, you'll have to unlearn that if you move up enough to where opponents will take advantage of you. That's a few levels up though.

Of course, winning and having fun aren't completely inseparable, so it does come down to weighing your personal priorities.