I bought the baby used, and she had some marring on the feed ramp.  Nothing major, but not the shiny polished look that I would prefer.  Any ideas for using a Dremel  or anything else to gently polish this thing?

It's a Glock, go shoot a few hundred rounds through it.  If you have no problems, then I wouldn't worry about it.

Have you shot some rounds thru it to check for functioning.  If there is no failures to feed or extract, don't mess with it.  People are too obsessed with looks.  If it works, don't fck with it.

I agree with the afore statements, but I must admit that I did polish the ramp on mine.  Used a dremel w/the polishing compound they have, and the hard/soft lollipop lookin' mandrel.  It's like a mirror!  Would my GLOCK have functioned PERFECTLY without this enhancement?  You betcha.  But I wanted to.  Point being: it is probably NOT necessary, but nor will it hurt it.

Get a felt bob for your dremel and some of their ruby polishing compound they are usually in a kit. Polish the ramp staying away from the chamber area. I have seen glocks with feeding problems from the rough ramp.

Field strip your pistol. Take the barrel and put it in the locked position in the receiver (frame). Insert a mag with a round in it. You will see they are very much in line. It is almost a straight shot into the chamber. If it makes you feel better, polish it lightly with Flitz and a soft cloth. Don't Dremel, or in any other way grind at the surface. The barrel is Tenifer coated, just like the slide. That is why Glock barrels have such a long life. (unless you shoot reloads or lead bullets, like the owners manual says not to, which is why Glocks go Kaboom, failure to follow instructions)
BTW-I am a 2 time, about to be 3 time certified Glock armorer.