Your warranty is good for the life of the pistol, so sending in a warranty card would be redundant... in fact, I don't think SA evens offers a warranty registration card for you to fill out, because why would you? The warranty is forever...
Polishing the feed ramp, from what I have read, will not void your warranty.. as long as you don't remove any metal... if you use a dremel buffing wheel, or a cloth with some buffing compound (like brasso, or whatever) you can get that thing as shiny as you want!
Raymond