I need advice with how to improve scores once in the 30s range. How long/ how frequently should I study to go from a 29 to 32?
my scores
C: 29
E: 34
M: 28
R: 29
S: 26
I just finished going through what you described. I had a 27 my freshman year and then 29 and got it up from there. It looks like your math and science scores are your weakest points. I can’t give you much advice on math because it was always my lowest and much lower than my other scores. One thing that definitely helped though was Khan Academy’s practice. You can pinpoint specific concepts you are weak on and practice problems from those areas. I would study as much as you see fit without “jabbing” a bunch of forgettable information into your head. For me, this was about 12 hours a week. At some point it is important to just rest your brain. Regarding science, I would say to work on your reading comprehension by simply reading a lot. In my experience, my science score repeatedly went up with more reading stimulus. In fact, I would argue that the science area of the test is simply another type of reading test. Heck, I use to have a friend who would change any variables on graphs to kittens and puppies. I don’t necessarily endorse that (lol) but find what works for you.
That was definitely longer than I thought I would write! Sorry if I got too off topic. I just want to help 
You need >9 section score points to get 32 (31.5). Think about where you can get those 9+ points. Science may be the one section you can get a boost after practice. It does not involve much at all scientific knowledge but just data interpretation. Simply doing more test and get familiar with different type of questions will get you better score within a short period of time. For Math, you also need to do as many practice test as possible and make sure you go through the answers and understand how the answers come out so that you can get the correct answer next time when you encounter a similar question.
A boost from 29 to 32 over the summer is feasible.