Think the others have largely covered this off, but heres my 2p's worth.
It can sounds quite harsh up the top end of the rev range with the stock exhaust, but get this swapped out and an UpRev map and you dont *have* to go anywhere near it, just ride the bundles of torque and off you go.
Tyre noise is annoying, and its purely down to the tyres themselves IMO. When you hit smooth tarmac the tyre roar dissapears instantly. I think new tyres will solve this. Also the new MY2011 cars come with tweaked sound deadening and suspension to try and help this.
With respect to long trips. I did around 800 miles over the recent Wales weekend and loved every minute of it. Also, we are going to France later this year and are taking the Zed. That will be another 1.5k miles put on it at considerable expense, but one I want to make as I want to take it with me.
So for me - go for it - you wont regret it - just get a new exhaust and UpRev map to make the most of it