Hi Hugh - Yes the 3 years free servicing on offer at the moment is a good deal. Unfortunately the cost of buying a new one was a bit more than I wanted to stretch to for a new WRX.
Are you looking at a WRX or STi?
I know someone who bought a new STi recently and they are struggling to get as good fuel consumption as me

With a new WRX I would expect the figures to be similar. I know that 30mpg is technically possible but I have yet to meet an Impreza owner that has achieved it ecen with the sort of driving you mentioned. I would think that at steady motorway cruising the best to expect would be high 20's. If you then get more that's a bonus.
I was a member on a couple of the forums and used to go to a few meets so i have met a lot of scooby owners with varies models of the Impreza. If you want any more info let me know.
Ian