On the other hand I get what you're saying, because usually your score reflects how hard you tried and not how smart you really are.
Standardized tests really only show how well you can regurgitate what you have learned over the years, and to some extent your critical thinking skills, relative to others who took the same test.
I think they are good at weeding out the really hapless among us, and pointing out the extremely bright ones. I am not so sure they do much to tell us all that much about the other 90% who take the test.
My guess is that trying harder will get you a better score than not, and it is clear some people are better test takers then others, but overall I suspect that it does not make that much difference. Most smart people have learned over the years how to take tests, especially multiple guess type questions, since usually at least one or two of the answers given are so far off you can eliminate them as possible answers. That takes it from being a problem solving type exercise to one that merely requires you to prove an answer is not correct, something that is often far easier.
Essay type questions are often easy to game, since all you really have to do is come up with a coherent few paragraphs to get a good score, but it is amazing to me how few people can do that.