I've taken the SAT twice, and I have an 800 on Math, but my highest Reading and Writing scores could be improved (770 and 660 respectively). I think I can get an 800 on the Reading section, and I'd like to raise my Writing score into the 700 range. Is it worth it for me to retake the test to earn a few extra points?
Check the average SAT scores at schools where you plan on applying to see where your current score falls. If a school's 75th percentile score for admitted applicants is the same or lower than your current score, raising it will have less of an impact on whether you get in or not. Don't take the test again if you're above the 75th percentile score for all the schools where you plan on applying.
If that is not the case, and you could stand to improve based on the statistics, I'd advise you to take the SAT a third time (as long as it doesn't interfere too much with your other schoolwork). Before you take the test, make sure you're very confident that you can improve your scores. Note that you will be taking the new version of the SAT this time, so you may see a significant difference in your scores. Take a practice test first!
If you end up scoring lower than your current score based on conversion estimates, you might decide to avoid taking the test again in its new format. However, from the information you've provided about your scores, it sounds like you are likely to do very well on the new SAT. Since there is no separate Writing section out of 800, your Math and Critical Reading abilities will count for more.