IMHO...
Too expensive to consider it a warranty. More like a "pre-payment" plan to replace your appliances as you could almost replace every one in your trailer for $1700. I wouldn't bother.
As far as trailer appliances, they are reasonably reliable but ultimately it depends on how they were cared for.
Your 3-way dometic fridge will last a very long time if it was primarily run on propane. Sometimes the electric heating elements fail, but its not uncommon to see units >15 years old working flawlessly.
Propane range/oven and propane furnace...will probably outlast the canvas.
Propane W/H last a good long time if cared for but as with anything in the water system, corrosion is your enemy.
A/C really depends on how much its been used and how HARD its been used.
In short - "it depends" but if everything works now on your 2003, you are probably in good shape for a number of years.
Enjoy!