Excellent topic, keep it going!
I own a euro spec SXT 2008 2.0 CRD and the only thing that bugs me is the engine noise. I guess the main cause is the fact dodge has used a non common rail VW diesel for the journey and used a alluminium bonnet. I'm considering the bonnet liner you mentioned and also having the wheel spaces isolated by a specialized garage that does these jobs. I've noticed that almost every euro car has these spaces isolated by some sort of meshed fabric. I reckon that this is for sound proofing.
In addition, I am also thinking about having the roof isolated because of the noise generated by hard rai. It almost sonds as if you're camping in a trailor.