On our Protege5 I spent a ton of time and money on sound deadening and the one thing that made the biggest difference was finally getting a quiet set of tires on it. I went through a lot of different ones on it too, unfortunately because so many reviews were with heavy cars that are quiet anyways. When we first bought our 3 last fall the first thing I did was swap out the tires (and then I added some sound deadening too).
The road noise and ride are my biggest concerns with the next car and unfortunately, they aren't always easy to get a read on during a test drive as some noises only get noticeable and annoying after awhile and some don't show up until you get on the wrong pavement.
Old thread, but which tires did you get that are quiet? I have a Mazda 3 Sedan and just replaced the crappy oem Bridgestones with Yokohama YK580. The new tires are much better from a driving standpoint but on certain types of road the noise is deafening.