I've had PPA for about 4 years now and save more then the cost of the membership every year. In fact I am in a nice PPA park right now (Amana Colonies RV Park, Iowa).
If you only go on one long vacation every year and then camp close to home, it may not be worth it but if you camp(RV) spring, summer, fall, then it will. I full time and travel all over.
You can visit their website and check out some of the parks in their program. I usually look in their book to see what's in the general area I will be stopping, then look in rvparkreviews.com to see if it gets good reviews.
You should also understand that some places will not honor PPA for more then 1 or 2 nights, and maybe not on weekends.
One of the nicest RV parks I've stayed in is a PPA park - Cochise Terrace RV Resort, in Benson, Arizona. Rated 9.1 on rvparkreviews.com