A Plan don't do agreed value either. I could only find the two main UK insurers who did Agreed Values ON IMPORTS.
Alex, its quite a difficult one because you have an Auto. There will be a hit to value on that alone. Look at the difference between manual and auto S14s. Its further complicated be the fact that there are no newly imported Spec R Autos, due to no model report. This will also have an effect on resale value
I bought my Spec R for ?13k and have added over ?7k worth of mods. However, my Agreed Value is currently ?14k because that's what I would sensibly expect someone to pay if I held out long enough (and possibly if I removed mods). Just look at how much Meddy let his go for, and he had similar mods at the time... I'm also going on how much it would cost to buy a replacement from an importer.
Going on your details, and the lower mileage, I'd say ?11-12k is a good figure, although I think you may struggle to get that if you sold.