Just a thought whilst reading this, is that after all the checks, if the steering is still heavy and lifeless, you could think about changing just the front wheels to narrower rims and 165's, using the correct offset and assuming they weren't too recessed into the wings, leaving your standard 195's on the back.
This would save some money and leave the rears to fill the arches. The trouble is, you would need to borrow a couple of 4/4 wheels to try, otherwise you won't know if it is successful or not. Maybe your local dealer would help with a loan?
