Question about cleaning the back of itouch.

The back of the iPod Touch is a highly polished stainless steel that can be scratched by looking at it the wrong way. It is virtually impossible to keep it in factory condition. Tiny scratches happen even by handling it with dirty hands that might have abrasive particles on them.
This pristine factory finish is all but impossible to maintain, but can be somewhat restored by CAREFULLY hand polishing it with a high grade metal polish such as a jeweler uses on gold or silver jewelry. The problem here, is being very careful to not get any of the polish in any of the iPod's orifices. I would put a tiny amount of the polish on a soft, clean lint-free cloth (microfiber prefferably), and hand polishing the metal surface. I'd be very careful around the black wi-fi antenna area and avoid getting the metal polish there. Still, any scratches more than very fine surface scratches are almost impossible to remove.

I wouldn't suggest using a polish. But using a polishing cloth (if you purchased screen protectors one likely came with them or you may have one that came with other products) tends to work well at getting it back shiny. The scratches you have are likely to remain if they are scratches. I know many complain about the backing and how it easily scratches, but I have a 1st gen nano and a iPod Classic, both of which survived with very few scratches. Having a case is key to cutting down on lots of physical damages....your Touch will be fine even if it gets a few scratches.

Metal polish takes forever, but it works.

I've used Brasso with success, though it is virtually impossible to get it looking completely new. Don't be overly aggressive with the polish-- it can wear off the text on the back of the iPod.

Prevention is by far the better route-- For the last several years, when I buy a new iPod I immediately add an Invisible Shield or Best Skin Ever to the back. They are a bit tricky to apply, but once they're on, they're on. It doesn't look quite as perfect as a new, unscratched back-- but that look only lasts 5 minutes anyway. 🙂

Silcone isn't going to completely protect the back from scratches.