Allow me to weigh in on this subject. I was in your same position and understand how frustrating it is. If you have worked on RC for so long, implemented every possible strategy, and still have no improvement, I wouldn't expect any improvement at this point. I always missed 7-9 in that section after trying every possible technique with no improvement. Thus, after taking the LSAT twice after considerable RC practice with no improvement, I've come to accept my 162 score. This is why...
Reading compreshension is a product of verbal intelligence and working memory. Oftentimes, individuals with learning disabilities associated with reading comprehension are shown to have verbal intelligence scores something like 6+ points higher than their working memory scores. Obviously, you don't have any sort of learning disability and neither do I. But 2 years ago, when I was diagnosed with ADD, I had to take the WAIS-III intelligence test, which showed that my working memory was a statistical weakness, something like 6 points lower than my overall verbal intelligence. I strongly believe this explains, at least in part, my general weakness in RC yet strength in the other 3 sections.
I also know that it is not possible to make noticeable improvements in working memory. I believe this may explain why most people who have not made drastic improvements in the RC section after tons of practice probably never will make drastic improvement due in part to a fixed working memory that inhibits complex reading comprehension in such a short amount of time as on the RC section. Those who miraculously improve on the day of the test may be lucky enough to get passages with familiar subject matter.
Can someone else weigh in? I think this logically makes sense but I'd be interested to hear what others think. Bottom line, I think you're wasting your time reading scholarly articles and the Economist. That is only going to help you in the sense that you may become familiar with certain subject matter that may possibly appear on the LSAT. And the chances of that are remote. If you want to improve your LSAT score, you're better off working to perfect the other 3 sections. Or if you're daring enough, try taking some creatine! There's a recent study out that shows it can drastically improve short-term memory.