Anecdotal evidence is what it is, but ours is similar to RJM's. Our 2015 plans to apply to some highly selective schools. His SAT scores were well below the mean at those schools, while his ACT composite was a 31, which is at or a little below the mean. Before retaking the ACT this summer, along with required single-subject SAT's and the AP Physics test, he did 4 hours of private tutoring and 6 hours of group tutoring with an independent guy who was recommended by other parents. I overheard some of one of his sessions, and besides very specific help on what to expect in terms of ACT questions as well as the AP and SAT tests, he did a lot on strategy - when to guess, when not to guess, which questions to skull out and which to skip over and get back to, how to identify various types of reasonable yet wrong answers, etc. He also did practice tests, as he had one before his first, untutored round. It was expensive, but the result was a 34 composite ACT, which puts him well over the mean at the schools he wants to apply to, including a 36 in math, which could help him a lot at those schools that super-score, which is pretty much all of them. He did well on the SAT and AP tests too, but those were his first attempts, so they're not so relevant.
Like I said, it was expensive. But if he gets into a school he wants to get into, and they give us enough money, it will have been more than worth it. We'll know in a few months.