Looks and sounds like a great car but I would check with Lexus that the correct services have been carried out as it's easy just to get stamps in the book for oil changes alone, if it has documentation/bills to back it up even better.
Depends how much you want it and if you are willing to pay a premium for the car, I paid top money for my Sportcross because it was low mileage and it had a checkable history but I still had a few expensive niggles, but at the end of the day I'm really pleased I paid the extra and got the car I wanted.
To be fair, how many LS400's are out there for sale with that sort of mileage.
Good luck in whatever you choose Jonathan.