These are difficult sentences! In the first one, "partial" is not the opposite of "impartial". It is the opposite of "complete". "The sublime" probably does not refer to the **concept** of sublimity, but to the property of being "sublime". "Precedents for the sublime" probably mean past examples of things that turned out to be sublime. It could also refer to places or landscapes that inspired others to produce sublime artistic and literary works. In the "if" sentence, "missing the point" means failing to understand what you were supposed to understand. Let me assume that "psychogeography" makes people walk through urban landscapes and imagine their own relations to various sites. As you are going through these places, maybe you will try to understand them all as a whole -- to "put them all together" -- and feel frustrated because that doesn't seem to work. But if you do that, this means you failed to grasp why -- you "missed the point" -- you were walking through that city in that way. In other words, putting all these places together into a coherent whole is **not** the point of psychogeography. I'm not sure my explanations are clear! The original sentences are written in very evocative language, so without further context, it's difficult to be perfectly clear about what they mean.

The following is my understanding of your passage. My biased understanding! Psychogeography is a subject that is intended to teach readers what the sublime is. However, the sublime is like “the ideal.” It is out there, but it is intangible. You can only imagine it. When one day you feel you have a grasp of it, you’ve got it. Therefore, all the obscure places, elusive effects, and precedents (putting all of these together may make one frustrated) are means through which we get to know what the sublime is.