I think YOU must have been mugged in the first place then bud.

The shock can be had fairly cheap but if it's been resprung and re-valved already, this is where the majority of the money lies so it wouldn't be too bad.

I'm currently eyeing up a Nitron race shock in the local bike shop

Well it was perfect in my bike, so £160 for a good shock ain't a bad price in my eyes. Especially after eBay fees! I had no complaints. I never felt robbed and the guy who bought it got a 10 month old shock all set up for his bike which was far superior to standard with no mods needed other than loosing the undertray. So I can't really understand all the fuss? The only trouble with it was that the guy bought it before deciding if it was what he really wanted. That doesn't entitle him to his money back does it? We've all bought things that were not what we wanted. I sold a hrc derestrictor I got for £30 for £135 now that was getting mugged, same as the other 3 people from here who sold them for the same! The moral of the story is check and be sure before you buy not after when it's too late. He never got mugged, he bought exactly what was in the add that's his own fault isn't it, no one forced him.

I've asked this before and it wasn't answered. Why does the GSXR or 600RR shock need revalving if it has the correct rate spring for the NC on it?

...the valving is different for the type of mounting and bike weights etc....the spring can be changed but the internals need to be able to cope with the fluid transfer through them too as this is what gives the correct damping. If the flow is too high then the damping will be too soft and if too low then then it would be stupidly hard..... from what i understand anyway

That's what I don't get. If you put the correct rate spring in the shock (I have an 875lb in my 600rr shock), then you why would the valving need to be done? It's going to have essentially the same movement as it would if the shock was in the 600rr, so revalving is pointless. Unless you wanna track it and get the absolute max out of the shock.