That is entirely up to you. You have to be the judge. Does it work properly? Is it so loose that it feels like it will fall off? Can you live with it the way it is? These are questions that only you can answer. Remember this too...you could end up with a phone that has a nice firm power button, but may have other strange issues that are even more troubling. So then, if your phone works properly, and the only issue is the loose power button, then I would stick with it. However, if all you can think about is the loose power button and it drives you crazy...then by all means get it replaced/repaired and hope for the best!
