Heavyjeffd - No you do not need to be affiliated. You can be independent, so you could work for youself if you want all the legal hassle, or you can freelance, go work for one shop one day and move somewhere else the next OR
DO the course if you really want to learn it, pay your on year fee, the just keep your card. You will still be a DM in knowledge but for those that dont want to teach you can just carry on diving. We (PADI Pros) know that to have a DM card, even expired, means you have to have done, OW, AOW, EFR, Rescue.
Also check the prices for the specialties. Some shops do very good prices, where the extra stuff you learn is very little compared to the cost of the dives themselves. Here for the deep it was the cost of 4 normal dives, plus the materials (about 40USD in books) plus another $50USD. So if you are going on a holiday and going to be doing a bunch of dives, find out how much extra to make them count towards something.
If you did hook up with your local dive shop maybe you could trade working hours with them for specialty instructor to teach you some specialties?
As a sidenote, i cant really tell from your posts if you want to do this so you can help in an official capacity or just want to expand your knowledge. You dont have to be a DM or Inst in order to be able to help other divers. When i did my Instructor Development Course, i was able to help most of the people in my class simply because i had trained with another agency and done different things, different techniques and able to offer alternative solutions to problems. Maybe instead of looking up the PADI ladder, look across to other diving types, maybe even into technical.