If you spend a great deal of time traveling, then I would say yes. They usually have all types of discounts at hotels and food places that you will get for joining and you will get special towing benefits for traveling cross country instead of just within your home state.
If you want a chance to meet other people who like to do this type of traveling around then join the club. They can offer you tips, tell you the best places to stay, give advice on the best things to take with you, and other useful things that cross country travelors need.
It is a good idea to belong to a good cross country motor club if you do a lot of traveling. It will help you with road side assistance if your car should break down, or you have another type of emergency like running out of gas, or locking your keys in your car.