In September we are taking our 2004 SC430 on a European road trip to Mercia in Spain and back. Storage space with roof down inc. the rear seat is good enough for two of us for the fortnight, but it is a convertible, so space is limited and as with the Merc. ingenuity can be required!.
imho roof seals are good, the drivers door seal around the mirror housing/tweeter can wear out so worth checking and replacing, as with all roof seals. Currently it's my daily driver car and has never let me down (wood firmly being touched!).
In my experience tyre noise is really about the tyres chosen. Continentals on mine are quiet enough for me, and I too am picky.
I would be more concerned about service history than mileage particularly. It's a great (verging on bullet proof) V8 engine and ancillaries. Just make absolutely sure the serpentine belt has been changed and that the car has been cared for. Later models have improved autobox and bluetooth etc.
In the end it is a convertible, so limited space, great comfort, great engine and relaxing to drive. Good luck with your research...
M