I've just bought a 2013 RX450h Luxury with 55k and plan to run it for 3 years at 10k pa.
My last car was an IS250 and I opted for the extended warranty on that at £895 for 2 years (IIRC?). Under the warranty I had 2 rear callipers, 1 headlamp assembly and a water pump replaced, all inside 15 months of ownership and under 45k miles ! Total value at Lexus prices around £1,600.
I haven't a clue about reliability on the RX, but I've opted for the warranty as it's so comprehensive it gives peace of mind. If I have to claim, then that's fine....if I don't have to claim, that's fine too, just means I have a very reliable car. I probably won't get burgled, but the insurance policy I have gives me peace of mind. Don't forget you get the full AA roadside package as part of the warranty too.
Hope that helps Nick.