I have a 02 focus 1.8 ghia tddi colour Moondust Silver, TBH I can't remember the last time I put a good wax on it, over 2 years I think, health problems for a while stopped me although it would get a jetwash from a local jetwash company once every two or three months I hear the detailing guys screaming WHAT !! :)
Fortunately the paintwork still looks in good nick (wonder if it's the colour) no rust anywhere, perhaps I got a good paintjob at the factory so it never really looks mucky but running the back of my fingers over the paitwork I can feel the roughness.

I've been reading up on Greased Lightning Showroom Shine which seems to have great reviews, my question is do I need to apply a good wax on the car after using Showroom Shine?

Thanks

looks like the product is more of a cleaner so apply that first and then the wax to protect the paintwork.

If you can buy a clay kit (meguairs kit from HALFORDS is about £25), wash the car then clay it, you will be surprised how much more dirt comes off it, the paint will be as smooth as glass, Polish then wax,