Obviously removing any unneeded weight will increase fuel economy & even performace.
The IS200 has quite a poor BHP/Ton ratio, So i'd be interested to see if there is any dead weight anywhere that can be lost without sacrificing anything useful?
I thought about removing the spare wheel and tools, as my last car was a clio 182 which didn't come with it.
However it'd be embarrassing to get a flat in a car meant to come with all the gear, I decided the price of runflats would defeat the object!