I have found tons of mods for the xB. SO far I have a header, high flow cat, stainless 2 1/4 exhaust, momo tip "muffler" (lol, the only thing it muffles is speed bumps), Air bag coil-over rear coils, STR 1.3 gallon fast-fill compressor with dual levelling switches, front anti-sway stiffener ( TRD ), MSD high fire ignition and wires, Fastman matched flow injectors, BSD rear disc brake conversion, custom class II hitch ( for towing my BBQ trailer ), Blue ox base plate system ( to tow it behind my motorhome) , Colgan custom carbon fiber bra, short throw shifter ( TRD), heavy duty clutch plate ( TRD ).
When TRD releases the 4 lb. supercharger early in '05 I am going to drop the $3800.00 for that, as it won't void the warranty. No way I'm going to add NOS during the extended warranty period.
I thought all the mods were going to kill my gas mileage, but I am still averaging about 28 MPG between hard city and freeway driving. It tows like a dream behind the motorhome.
As far as interior room for big guys, this thing is HUGE inside. It is like it is built for 6'5" drivers and rear passengers. I am 5'10" and built fairly thick. I am swimming behind the steering wheel. The back seat is even bigger. It is WAY bigger inside than outside.
Good luck and have fun with it.