OP, ..."3. If it sounds really good, leave it alone!"
That is a good one. I realize, typically I get to the point where I am really happy. After having gone through an upgrade cycle. I've done the cables, speaker adjustment, etc. Then I leave it alone... for six months or a year. So I know the sound inside and out. Then I work on speaker placement again...or vibration control, or some aspect I have not really worked at. And I get a notable improvement. My skills for fine tuning have increased after really spending time with my system. Then I leave it for another year and then attack some other aspect. Over time... it just gets better and better. This assumes, you have gotten all your components perfect and synergistic and are happy with them.