There are some worthwhile hotel discounts with AARP, particularly in Europe with BestWesterns. 20% adds up to a free night over the course of a week stay, and they have some good properties over there.
Of course AARP is designed for the needs of American retirees. And most here have similar rate benefits for rental cars and other hotel chains through their businesses or elite status programs.
CARP used to have an additional discount off AC fares, but I don't believe this exists any longer, since AC has made such discounts more widespread.
Remember, these organizations are primarily lobbying entities to advocate on the part of the members. The services and discounts are a sideline to lure more members so their lobbying efforts can be said to be done on behalf of many more people than would otherwise join such an organization. Keeping the fee to $10 to $20 a year also makes it affordable.
Both have monthly or bi-monthly magazines and newsletters as well with articles they feel will be useful for their readership. Increasingly, they are dealing with issues affecting "younger seniors" in their 50s who must cope with their "older senior" parents in their 70s and 80s.