My thoughts echo those of pseudopianist regarding Prelude No. 4. I would take it slower and enjoy all of the beauty of it even more. The melody is more important than the chords in the left hand, and the melody needs to "sing out" more. What exactly do I mean by "sing out"? Well, imagine the melody being sung by a beautiful, resonant voice of a soprano. She will come out loudly over the rest of the accompaniment. The piano is obviously not a voice due to its decay and lack of vibrato, but the simple act of "picturing" the sound will help you achieve a more musically mature performance.
Prelude No. 20 sounds good. You also want to think about bringing out the melody and the moving voices more, but this is an entirely different question because the melody is part of a chord - you have to bring out one note over three others all in the same hand at the same time. This requires a lot of discussion, but I distinctly remember there being a good Bernhard post about "voicing" that you might want to check out. Also consider greater dynamic contrast in this prelude - louder ff's and softer pp's. (Although this may also be due to the kind of piano you were recording on.)
Keep up the good work!