First off, what is the extended power train warranty? Are you trying to extend the 100,000 mile coverage, if so for how many more miles/years? The PT warranty covers far more then just a blown motor. Simple thing like a leaking rear main seal, covered. Leaking valve cover gasket, covered, failing internal transmission issues covered. So don't just assume the coverage will only be there for the blown motor.
Secondly, at 100k, i'd be surprised that the extended coverage would go much past 136 or 150,000. So for $3000, it may not be worth it. Once you get 4-5 years under your belt, and 100,000 miles or more, the Cadenza is only worth between $6000 and $7000 tradin for Lux and above depending on condition, and even that is probably high. So to get a coverage for $3000 or roughly half the value of the car, especially considering it doesn't cover other important things like starter alternator, radiator, AC parts...that's just too much money I think.