I bought a Nissan Quality Guard 4-yr/48k warranty on my VX when I bought it used (from an Infinity dealer) with 45k miles on the clock. Paid around $2k for the warranty with a $100 (per visit) deductible. It paid for parts and labor for anything that needed replacing (if it was in need of cleaning or adjustment only, they did not cover it).

In the end, the warranty paid for about $2700 worth of repairs in that time, so it worked for me, but like $1400 of that was for the rebuild of the rear differential due to an annoying but probably innocuous intermittant squeal. Without that repair, I would have spent more on the warranty than it cost me, so it was aclose call.

Here's important info - a dealer marks up the warranty just like any other part. You should be able to bargain with them on the price of the warranty. Make sure you let them know that for you, it's either they sell it to you for $1900 or you don't buy one at all. That's the only way they will budge...