I bought a used 05 RX330 Sports Luxury (Nav, Mark Levinson, RevCam, B/Tooth, Leather, Roof,etc) last Feb with 90km (56K miles) on it and was very surprised how well it drove. The local dealership loaned me a demo RX350 with 5 000km on it while mine was being serviced and apart from the heated seats and the updated Nav it was very difficult to pick the differences between the two. My friends & family drove it & thought it was new until I showed them the odometer.
Mine now has almost 100 000km (60K miles) and I have only have a rattle in the cargo blind when the auto retract clips near the tailgate are not latched.
It is OK on fuel - I recently drove from Melbourne up past Sydney & back, a 2200km (1400 mile) round trip, and averaged 10.1L/100km (~23MPG) with luggage and 3 people in car with freeway conditions 95% of the way. Not bad for such a heavy car. My last car was a Holden Calais (www.holden.com.au) , which is almost identical to your Pontiac G8, with a 5.7L LS1 V8 and the best it ever got was around 9.5L/100km (~25MPG). I miss the raw grunt of the V8 but the pure luxury & refinement of the RX more than makes up for it.
All Lexus sold new in AUS are Japanese built and all RX's are AWD, although there are a few used Jap "grey imports" getting around that are re-badged Toyota Harriers. The local lexus web site will give you more info on our specs (www.lexus.com.au). You will notice that only 2 packages are available and options like radar cruise, homelink, sat radio, air susp & a few others aren't available. Build quality & reliability here has a reputation of being much better than BMW, Audi, Volvo or Benz (some models are imported from South Africa but I think X5 & ML are US sourced) and the RX has won the most sales of Luxury 4WD market here since it was realeased to the AUS/NZ market in 2003. The series 1 RX was never sold new here.
I am dissapointed to hear that your RX has issues. I called the previous owner of my car (she traded it on an Benz ML at end of lease) and she never had to have a spanner put on it. It is also worth noting that a new Sport Luxry model here cost around $90k with on-road costs ($AUD is almost on par with $USD at the moment) - I'm unsure whether that has an affect on bulid quality or not.
I'm happy to assist by comparing & sending pics of components, (eg brake booster, etc) if anyone wishes.
Good Luck.