For the spiral enemies there is a pattern to figure out, it's just a rather confusing one, but that's on purpose. One thing to keep in mind is that they always spawn in front of you, so once you find the safe spot you can abuse it every time.
As for milking early sectors for points, that is intentional. With later sectors the game gets more difficult, but you also earn points much much faster. Not to mention that the score you earn gets multiplied more sectors you cross, which is also kept track of.
Ignoring the sector 9 boss is also intentional. Defeating bosses give you a lot of points and a shield so there is an incentive to defeat them, but if you really want you can just focus on the rings and skip the sector without even defeating them.