I can only tell you of my experience with this stuff which I used on black plastic trim with really spectacular and very long-lasting results that gave a very even finish. It does make the plastic look 'new' ie not too glossy and not too matt.
I applied it to the wing mirror mounting trims, the scuttle panel below the windscreen, the door bump strips, and similar strips around the bumpers.
I applied Forever Black shortly after this thread began, in spring of 2012 and can tell you that the the above mentioned sections of trim are still very black to this day, in spite of regular snow-foaming; pressure washing; and weekly bucket wash.
Polishing using Autoglym Super Resin Polish will leave a white residue if you aren't careful about avoiding the black trim, but Forever Black seems to partially protect that from happening to a small extent. Waxing with Collinite 845 seems to have no real effect and leaves no real noticeable white residue.
I may however 'sharpen up' their appearance with another coat next summer. It's a slightly time consuming job as you have to mask off the bodywork first, (I used a low-tack blue coloured masking tape from eBay) but I feel this is a small price to pay for such a good result.
I would doubt that this product will work on your metallic items, and if it was me, would look at renovating by properly repainting with a suitable paint that matches the original sheen - except do it better with some undercoat!
You might be right about using Colour Magic - I don't much like Colour Magic but have used it on my wife's car to cover over the scratches and scuffs that she has managed to induce, and while it seems to work as a polish/filler it does need a couple of layers of wax over the top of it to 'seal' it.
I haven't used 'Autoglym Black dye' as Sgould has - but from his photos the result looks okay but not as even as I would have liked but he does mention he felt it needed to coats if really badly faded
Let us know how you get on