I am fully capable of going -0 on games. When I do miss questions, it's because of dumb errors from working too fast (like circling the wrong answer or misreading a choice).
For LR, I miss the hardest problems. So, for my second take, I did the hardest LR problems of every section, and saw zero improvement. However, I think going through the Manhattan book and using their forums for this take will help me improve in that area.
RC is a different beast. I can feel like I completely understand a passage and still get questions wrong. A lot of the times, it''s the abstract questions (what would be an analogous title, what two words express how the author feels about this, etc.) and certain inference questions that I get wrong. But I have been doing well with my review this time, as I now treat most RC questions like "must be true" LR questions. With that said, my goal is to get every LR and AR question right so I can have room for error with RC, as I have yet to come across a meaningful way of gaining points in this area.
As for diminishing returns, I would not be taking this test again if I hadn't been wait-listed at six t14 schools. I got into two t14 schools so far, but I doubt I will receive much aid, if any. So my plan is to put a deposit down at a t20 school and take the June test. If it goes well, great. But if not, then at least I'll still be going to school in the fall.
On LG, totally understood and fair. I had this issue, and this messed me up on min/max (those would be more from going too fast and not bothering to check the answer... often on min/max there is one rule that plays with others to prohibit the more 'obvious' answer... I use obvious answer loosely, because it's incorrect)
On RC, I went from -6 on my first take to -2 on my second take, and one mistake on my second take was beyond ridiculous. I was averaging -0/-1 over several tests and sections leading up to my second take. You can improve here. It's about finding what you do differently on those -1 sections... there is going to be some difference even if not huge. For me, the difference was making sure that I went back to the text for every question in the section and reading the section faster. My problem originally is that I would try to absorb and retain (which I'm pretty good at) but fell for the traps they laid for people going too fast to check the text.
On LR, my only question would be whether you are rushed on the last few questions. If so, you may benefit from trying to institute a method where if you don't get it on your initial read through or two that you mark your best answer and come back, time permitting. I find this strategy helped me a lot, but that was more to break from mid 160s to high 160s/low 170s.