Short answer is to pass on the offer from your dealer. I was quoted $940 for zero deductible 8-year/75K warranty from Molle Toyota. I don't drive enough for 125K warranty, but I would expect them to offer a good deal on that as well.
Molle Toyota
601 West 103rd Street
Kansas City, Missouri 64114
1-866-557-9913
Jay Young
You don't have to buy from the selling dealer and you can buy it anytime before the initial 3-year/36K limited warranty expires.
Scott - the transmission and the engine are covered on the 5/60 powertrain warranty and you are unlikely to ever use that. However, you are fairly likely to have A/C compressor, navigation radio, ignition coil, radiator fan, heater core, blower motor, ECM, airbags, etc. fail.
(I think the ECM is about $1400 in parts, not counting labor. I think the navi radio is about $2200 in parts, not counting labor with core exchange - although if it came to that, I would replace it with an $800 Pioneer.)
If you don't do your own work and if you want the dealer to maintain it - it's a 50-50 chance you will pay about $1000 in dealer repairs over 8 years and 125K miles. It comes down to how long you plan to keep the car (if you sell it in 4-years, it was likely wasted money), and how much peace-of-mind is worth compared to having $1500 in the bank in case the car breaks - (and it could cost much more then $1500 over the term of the warranty)
http://forums.edmunds.com/discussion/8596/toyota/highlander/extended-warranty-toyota-extra-care
Also from elsewhere on the internet (this was a reply to a person who was considering between a Focus and a Corolla) ...
I have bought them on Fords - it's a good idea to get the $0-deductible and rental car plan. The reason is with that, you can just take the car in whenever something breaks. With a $50 deductible, that is per visit, so you tend to save things up until they break (The radio display is intermittent, but it's not a big deal, so I'll wait until a couple other things break before I spend $50 to fix it.
(Yes, you can get it at anytime while the car is under warranty, but on Fords, it is $100 more if the car is over 12-months in service)
7/100K $0 Deductible is around $1600 from Ziegler (on Fords) - I would expect Toyota to be similar or less.
As far as whether or not it is required - it depends on how long you plan to keep the car, how skilled you are mechanically, how likely you are to take the car to the dealer for repair, etc.
The factory warranty is 3/36 BTB and 5/60 powertrain on both cars. So essentially, you are paying $1600 to fix anything non-powertrain that breaks after 3 years and before 7 years. If you trade cars every 3 years, it doesn't make sense at all. If you can do your own work - it might be a $50 part that failed that it will cost $750 for the dealer to install that would be free if you have the warranty. Then again, you might pay $1600 and NEVER use it at all (my car oddly enough was more reliable AFTER the initial factory warranty ran out).
Also - if you are mechanically skilled - let's say your alternator fails. You can probably change it yourself and get a replacement at the parts store with a lifetime warranty for $200 or so. If you have the extended warranty, it is free, but once the warranty expires, you have to pay $200. If you hadn't had the extended warranty - when it failed the second time, the part would be free.
As far as whether it's necessary. Hyundai/Kia have a 5/60 BTB and 10/100K powertrain warranty. It wouldn't make sense to spend $1600 on a warranty for them. I said earlier that I would expect the Toyota to be more reliable than Ford, but if you thought the warranty was worthwhile on a Ford, I wouldn't say the Toyota will be so flawless that you will never use it. (I might not pay as much for it on a Toyota, though, as I'm not sure it's likely that $1600 will fail in the 3-7 year range.
You don't have to buy it at the selling dealer. I am more familiar with Fords, but my local dealer wound NOT match the lower online sellers price.
At least from Ford, the extended warranty DOES go up if you don't buy it in the first 12K miles or 12 months, but it only goes up $100 on usually a $1200-$1500 warranty.
One of my local dealers offers a lifetime powertrain warranty - it isn't through Toyota, but it doesn't cost anything extra (beyond the markup already in the car).
Ultimately - it comes down to what it costs and what you can do yourself on the vehicle and what you are comfortable with.
For example, Dodge has a lifetime warranty for around $4500. Somewhat unlikely you would spend $4500 on dealer warranty service no matter how long you keep the car.
Now - let's say the Toyota warranty is around $1200. If you don't do your own work, or want the dealer to do your repairs, you might or might not spend $1200 at the dealer. If you can do your own work - the $1200 in dealer repairs might only be $150 in parts and your time or $600 in labor at an independent shop. Or if you have $1200 - you could set that aside and use it for repairs instead of the warranty. Of course, if the car blows an engine or transmission or maybe A/C Compressor, you would probably have been better with the warranty.