If it's your dad's car I think you'd be a better judge than us as to whether it's a good example! :P
Seriously though looks a very tidy car, mine's very similar (same colour, bodykit, auto but has satnav and is on an 02 plate) and I was offered £4.5k by my Lexus dealer in p/ex a few months ago.
So I'd £4.5k is probably a reasonable price, but again if it's your dad I'm sure you can come to some agreement :)
The IS200 is not a great car on fuel, and the autos are even worse, as well as being quite slow. The box itself is a good one, but it's not a fast or economical car. I average about 23mpg, if mainly town driving don't really get better than 21mpg, although I'm not that gentle with the throttle pedal