Escalation is always a problem with the action genre. How do you keep up the tension...? Show a strong enemy... show the hero level up... show the hero beat the enemy... rinse and repeat. Eventually you'll get to DBZ levels of ludicrousness.
One Piece escalation is nowhere near DBZ escalation. I find new techniques to be reasonable in showing increased proficiency, compared to powering up through sheer willpower or something.
Possible minor fanboying, but IMO One Piece is currently at a peak as it approaches the climax, and it will be one hell of a climax considering just how many plotlines and strong characters are converging.