Scratches, whether from the edge of your music stand, the ring on your finger, or the dirt in the cloth you use to buff it up... are still scratches. Tarnishield (and the others) will remove the oxidation (discolouration) and leave a protective coating behind. The horn WILL look a lot better but not like the day it was "born".
HOWEVER... some scuffs and other evidence of use should be worn proudly... it means your horn isn't a "case queen" and you are actually PLAYING it. They don't affect the sound and can't be seen from the audience.
To your other question... there have been several posts in the past about cleaning your horn (keeping the slides "bright and shiny", valves, etc). Here's a starter
http://www.musichem.com/articles/trm...r_students.htm .