A bit strong on a 1999 import I'm affraid. You'll have to test the market. What goodies are on the car over others of the same spec ? What have you changed - all the discs will be corroded out by now, callipers about to pack up on the rears - they can sieze if not stripped down routinely - also change brake fluid every 2/3 years............the list goes on
Don't believe Glasses guide though, this guide is basically for people who want a more recent plate, almost regardless of mileage, Glasses is good for Ford and Vauxhall boggy spec car buyers. The CAP black book is much better.
Some folks look for low mileage, to get a deal on a slightly older car registration. Remember X and Y plates are only 3 months between. It's all about genuine mileage and service history with Turbo's IMHO.