Test scores are important at lots of colleges. But they're never important enough to sacrifice any of the following in the name of preparing for the SAT or ACT.
1) More money than you can afford.
You don't necessarily have to take an expensive course or hire a private tutor to improve your test scores. There are plenty of short courses, books and even free online test prep options. Effort expended is more important than dollars spent.
2) Time that could be spent getting better grades, or playing better basketball, or painting better pictures.
Test preparation needs to fit into the rest of your schoolwork and your life. Choose your time of year to prep wisely and apply some good time management when you do. If you feel pressured to ignore other important areas of your life, sacrifice the test prep first.
Some kids are not good test-takers. While they can certainly improve, efforts to transform poor test-takers into great test-takers usually don't work and make those kids feel badly about themselves. Put in some appropriate time and work hard to improve your scores. Even if you're not happy with your results, be happy with your effort. Then move on to other things you enjoy.