what can I use to keep the silver calipers looking newish, soapy water and brush doesn't move the stuff, will Wonder Wheels (see below) do it, you need to be very careful with products like these (I believe wonderwheels is quite harsh so I only use soapy water and polish on my new wheels) so what's best for calipers apart from painting them which I don't want to do.

wire brush them

yep good idea

problem is calipers will always rust so either paint them silver? let them go rusty brown? or wire brush them every weekend ?

Yes paint them silver or whatever colour you fancy