I think it sort of depends on your circumstances. If your family is really rich and willing to pay for college then money doesn’t really matter and you should spend time on SAT or ACT studying. If you need merit money badly though some schools offer a full ride for it. So I think it depends a lot on your circumstances.
Also, I don’t see how being “National Merit Finalist” looks impressive, because isn’t it based on test scores? If you have good test scores, then the college will be impressed by that? I don’t see how anything through National Merit won’t already be in your application(test scores, grades, recommendations, essay, etc). I’m not sure, maybe I’m missing something.