Hi,
I'm about to purchase a GS430 and have been researching a fair bit. We didn't get the GS400 in the UK but as I understand it the Gs430 is SII facelift only and the GS400 is SII pre-facelift only therefore most of the below list from the UK knowlege base applies (some is GS300 vs GS300 only), personally I'd say the larger brake master cylinder is reason enough as it's a known weakness at around 100,000m and a very expensive part. I'd also find the improved sound proofing and more modern (cleaner, more efficient) engine fairly convincing. The increased torque, esp at lower revs, makes for significant performance improvements in most "real world" driving conditions. If the ETC lag from the lights is an issue for you do a stage 0 tune (esp. MAF) and get a Blitz controller.
SII facelift changes:
Exterior
New rear light cluster design
New front light design
New front grill
New exhaust tip design
Interior
Chrome trim around gear shifter
New dashboard dial trim
New steering wheel design with larger chrome L badge
Colour of centre air vent and instrument trim revised
Front ashtray is now in wood rather than grey plastic
Different stereo, although seems the same quality as the older one
Sat Nav option upgraded to DVD based system with widescreen LCD display
Increased sound insulation
Engine
Improvements to economy and reduced emissions
Iridium spark plugs
Engine cover now fitted
Transmission
GS300 now comes with E-SHIFT, push button steering wheel mounted gear selection
Safety
Brake assist
Electronic Brake force Distribution
Curtain airbags
Double locking doors
Seat belt pre-tensioners
ISO-FIX child seat fixings in the rear seat
Brakes
Larger brake master cylinder
Suspension
Improved shock absorbers
Uprated anti-roll bar
Revised suspension bushings
Servicing
Service interval is increased to 10,000 miles from 9,000 miles. Cam belt change interval increased to 100,000 miles from 63,000 miles
