I don't think it's to high a price, it's effectively a new bike for £4k,
That's the same price as a new 250cc bike,
The problem being is that it's a limited market, and it still needs the suspension sorted as it was carp from new, using it will mean it soon drops into the normal price for a reasonable one, take my own, it's got just over 17k miles on it, it's in pretty good condition, but no where near as mint as this, however it will have new suspension and still be under half of what this one is on offer for,
So unless someone specifically wants this bike, then it's a difficult sale, as its competing against much cheaper gen 1 fazers and some good later generation 2 fazers,
I think that it is well worth £4k, but realistically if you really want to sell it, you need to lower the price a good chunk, don't look at what is offered on eBay, there are many dealer prices and over priced bikes there, they will still be there in a few months time,
That may be to hard for you to bear, I'm the same with my mint FZ6 fazer, it's to good to let go for what people are willing to pay for it, so 2 years on I still own it, despite not using it in those 2 years!
I note you have it up for sale on Ukgser!