I think it's a little of both. With my '04, despite replacement of the window seals, etc. the rattles persisted. I even had the one-way valve installed in the moonroof, to no avail. There was also road noise. That's not completely eliminated in the '06, but is noticeably reduced, I'm assuming due to better insulation. In addition, there are no rattles or squeaks whatsover, so I can now listen to the radio at a normal volume! I also noticed that with my summer tires (Pirelli Scorpions) the road noise was less than with my winter tires (Dunlop M3's), and I guess that's expected. I"ll be interested to see if there's a noticeable difference with the '06 once I switch to the winter tires.

As for the interior, it's not much different from the '04. The materials look the same, but feel a little less cheap. I got leather seats in this car as well, and it's definitely of a better quality than my '04 version. The leather both looks, and feels softer.