The economy on the 8 valve is hopeless when you consider the limited performance.
You'll do well to average mid 30's overall - I could eek mine to high 30's on a long wafting trip cruising at 50-55, but as soon as you hit traffic, it'll head back to 30mpg. And my GTi ran perfectly with none of the associated idling faults
Contrast that with my trusty old rusty TDi 90 (mk3) - I've done 235 miles when it reaches 3 quarters and no matter how hard I drive it, I can't get it less than 56mpg over a tankful. Oh - and unless you thrash the Gti, the TDi is actually quicker.
I now have a new Boxster 2.7, and I'm averaging 30.5 mpg - or 1.5 worse than my GTi and I give the porker more welly. Our old Boxster often returned 36mpg on a non thrashed trip.
Economy isn't the 8 valve's strong point - why on earth they reintroduced it to AUdi / VW / Seat is beyond me. It must have been a purely financial decision - or they didn't have sufficient capacity at the 20v engine plant.
The upside of the 8 valve is nippy performance at low revs (it feels like it gonna be quick till 3000 revs!) it makes quite a nice rorty noise and they are pretty damn reliable - after all it is a 20+ years old design.
I think we'd enjoy the car much more if the MFA was disconnected - I've found that with all my cars, the presence of an MFA guage tends to bring the Granny out in me!