I found that my NG 2.0 manual was actually thirstier than my 2.3 HOT Dame Edna. Perhaps it's the bulk of the car (longer and heavier) and the fact that even when the 9-3SS came out the L850GM engine didn't seem quite as efficient as the Saab H-engine (B2*5, B207) there was a lot of criticism at the time that the saloon was no more powerful than the hatchback (210 versus 205, and tuning the B207R was limited)...
Body and trim panels are unobtainium, rear lights, aero bumpers, exhaust are exhausted supplies. Exhausts have to be custom made (that's my forthcoming expense). Look at my thread on UKS regarding the windscreen.
Mine also has the U-rail in the back - use it to stop things flying around.
Have considered doing a Hirsch to 260PS but I would rather check that the engine has a lot of life left before spending money on the upgrade (I know of one 2.0T that has gone pop recently, sadly)
Not done the Infotainment upgrade, doesn't bother me that navigation defaults to Belgium.
Insurance no more expensive than on my old car - still paying the same as I was on a 1.4 Astra in 1991, stands to reason the 1.3-1.4 Astras are the fastest cars known to man