Im a Peer College Counselor...aka TA to the College Counselor. we are instructed to advise students to not take more than 3, because colleges will tend to average them after that. this is also repeated by UCLA reps.
however, like someone said earlier, it depends on the college. some will score them as a whole, others will mix/match your V and M scores from different testings. might also consider that if you improve gradually or even dramatically...it shows that you're "learning" and "maturing" overtime, whether that's true or not...
my tip for the SAT is to just familiarize yourself with the testing formats and be smart about it. those books should help you with how the tests are structured. be sure to know when to skip and when to guess--strategy, strategy, strategy. in my opinion, the SAT is more of a stamina test than anything. the longer you can remain openminded and analytical, the better you'll do. the second you lose energy, concentration, motivation, etc, you will begin to misread things. that said...rest your butt!