Hope I am not too late to add to this thread.
Definitely an emphatic YES to the extended warranty, however it really is worth shopping around all the Lexus main dealers asking for a discount or seeing what offers they may have. Dealerships earn commission/ have targets on warranty/service packages so they may be keen for your business? You will certainly be more likely to get a favourable discount if extending your warranty by 2 or 3 years depending on how long you were planning in keeping the car? In the past I have always managed to get discount on the extended warranty whether it be negotiating on its own or extending it by a couple of further years or as part of a service package. Trust me its well worth several phone calls!
Incidentally a couple of years ago I obtained a good discount (20%) by extending the warranty to 3 years rather than for one, I paid monthly so there was nothing upfront. Then when I changed my RX for a younger model about 10 months later, all I had to do was cancel the direct debit for the warranty with no penalty! (As with anything though- do read the small print first-agreements are changing all the time!)
Do your homework and save yourself some money!