Wow. Based on your accumulated miles, that cost is equivalent to paying over a dollar per mile for a warranty. That's like paying fifteen bucks a gallon for diesel, with the downside of not being able to drive anywhere with it. At 74k, that engine is starting to hit its stride. I would consider a severe maintenance schedule, using the finest fluids and filters including a quality fuel lubricant. I would take the gamble and forget the warranty. It's like betting that you might get hosed versus knowing you are getting hosed.