Service plans etc
Insurance is insurance. It is desirable or not depending on your tolerance for risk. Overall, the cost of the insurance is greater than the cost of the repairs paid for by the insurance. That is the bet the insurance (Service) company is making when you purchase a contract. They charge more that the expected cost of all repairs in aggregate. That is where they get their profit. This process is not new to you. You make this same deal when you purchase life insurance, health insurance, regular car insurance or a service plan on a dishwasher at home.
For years I drove an older class A motorhome with only liability insurance. No road service agreement, no nothing else and I did well. Understand that I had been rebuilding trucks with my dad since I was 12 or 13 and my wife and I drove every nail, installed the plumbing, wiring, etc in our 2000 Sq Ft ranch style home. I was not concerned with motorhome failure as I knew that I could repair it and because it was an old unit, if it was a total loss I could afford to scrap the whole thing and purchase another one.
Soon I will take delivery of a 12 year old 2001 Tiffin Allegro Bus and I will get Collision Insurance, and liability insurance. I will also have a roadside assistance/towing package. The collision because I financed this coach and the bank requires it and the roadside assistance because I am older and no longer want to be under the coach changing parts on the side of the road.
On the other hand I will not get any warranties on the the coach, appliances, or other items as I still figure I can fix most things myself and so long as the chassis runs I can get it home to work on it. I also figure that with only 40,000 miles on a chassis built to run 450,000 miles, and I really do the maintenance, there will not be a major failure. I may be wrong, but I am willing to take that risk. I could wind up paying for a coach with no engine that sits in the yard unused until I can afford the time and money to replace it. All it would take is for me to fail to tighten the oil drain nut properly.
So to answer your question about service contracts, etc, you need to take a realistic look at your abilities and desires then select the risks you want to take and which risks you want to pay someone else to take. Can you repair a rusted out battery compartment? Do you know how to check the tires for rot and expiration dates? Do you have the financial ability to tow it home at many dollars per mile if a freak wind storm blows you off the road and you break an axel? Are you willing to give up an entire vacation because of some equipment failure? There is no magic formula that works for everyone. Only you can answer these questions.
Note that I never mentioned the quality of the contracts available. Some insurance/service plans are great and others not so much. Look around in the market before you make any decisions and with your family choose the coverage you need based on the risks that are reasonable for you just like you do for life insurance, car insurance, etc. Many people do fine mostly self insured as I did with my first one, some need insurance against all perils because they are in bad personal health and bad financial health. You, like most of us are likely somewhere in the middle.
I hope this helps sort out which way is best for you.