I take my SC to France every year. Roof down you are very limited with space in the boot, and I bought some of the specialised luggage in the link below. Realistically long motorway drives you will have the roof up if you want to make some pace, so plan accordingly. As to Bluetooth, I added a Dension kit, see other link below. It's brilliant, limited only by the SC Mark Levison kit. It's also my daily driver, and I get most stuff into it somehow!
Agree with everything else above. Check any car you look at is on proper tyres and not the original run flats, they are very noisy. Later models have better gearbox and suspension, but are quite rare. Mine is an early model with later model wheels, which seems to work OK.
Servicing is normal Lexus prices, but not much ever goes wrong (touchjing more wood :) ). As above make sure the 100k/10 year timing belt change has been done if you go for that age. Budget for around £500 if you need to do it.
I did see the one rusty one mentioned, but it's the only one I've ever heard of and I think it lived near the coast all its life.
http://www.clublexus.com/forums/sc-430/42378-custom-fitted-luggage-for-sc430-2.html
http://www.lexusownersclub.co.uk/forum/topic/74681-ipodiphone-link-by-vaistech-soundlinq2-sl2i-up/