I have recently bought a 2008 RX400 with a low mileage. I have faith in the reliability of these cars as the above posts confirm.
Look at the worst case scenario and your options to change. £1,000 to keep a good car going is far cheaper than buying a replacement. Wear and tear items will be linked to mileage and age. With a Lexus you would be very unlucky to have lots of things go wrong one after another.
You know your car, check for corrosion and treat if necessary. We all come to a point when we say, enough is enough, I need to change this vehicle. When that time comes is dependent on the individual. The longer you keep your car the more value you will get out of it. You can't really compare older Lexus cars with other makes, as they are far more reliable. I would not even consider buying a BMW, Mercedes or Audi of this age. Spend the £1,000 and I would be very surprised if will not last another 30 months. You have already spent money on the larger wear and tear items - dics / pads / timing belt. You will have to spend a great deal more to replace your present car.
Keep us all informed about what you decide but I would be keeping it and putting that tow bar on. Good luck!