Firstly... Stainless steel scratches very easily, especially polsished SS which is what’s on the silver version.
Even brushed matte SS will show scratches, it’ll just be much less noticeable. Apple likes everything shiny so it’s pretty much why they went with the hey look at me finish for the silver model.
Now the space gray is a whole different ballgame since it’s coated with something which will make it less notable for scratches, looks pretty much like the Apple Watch. To the naked eye you won’t really be able to notice any wear and tear on the space gray unless it’s dropped, or dinged.
As for polished? I doubt the space gray can be polished with anything since it’s dipped in something to make it appear black. As for the silver and untouched band, Yes you can polish it. However and I say this with such caution, cape cod is a very dangerous product to use on an electric device. The stuff is no joke and the chemical is harsh. I have used it on my watches in the past for hairline scratches, and when I use it I have rubber gloves on and need to carefully place tape on the parts I do not want polished. This is on a watch, which may be a lot more expensive than a phone, but isn’t electronic and I only use it on the band, not the watch face or even really near it.
With the phone if you get that stuff on the screen or inside the speakers on the bottom where most of the scratches will happen, you are asking for some serious problems because that stuff will destroy your phone and I doubt using something like cape cod is under Warrenty.
