My dealer told me I could get it right before the current warranty gives out, for an increased price. What is it, like $1500 up front? Then it's about $3k (basically, I remember it being double) to get it just before the end.
I figured it was worth it to wait and see if I was gonna keep it that long, or want to trade it in. If I keep it, I fork out the 3k (I *really* want to avoid owning a new VW without warranty). If I want the newest great thing, the new buyer can figure out the warranty.
He did note that your driving habbits could help make the decision. If you're going to finish your warranty with miles, i.e. you drive way more than 12k a year, you might be better off getting it up front. Me, I drive about 9 - 10k a year, so he suggested I wait.
This is all from the dealer, so take it in knowing that.
I don't drive as much as some people, and the financial guy at the dealership asked me how long I anticipated having the car, and about how many miles/year I would likely put on the car. I told him that I intended it drive it for as long as I could, and he gave me my options. I opted for a plan that would take me up to 7 years, 70,000 miles, and it cost about $1000. Seemed OK to me!