For me, the diagnosis of PDD-NOS helped me understand my son, and validated my feelings that "something is different about this kid". I see the Autism Spectrum as a huge continuum of behaviors, symptoms, sensory and understanding issues. There are some landmarks, like Aspergers and Classic Autism. Some kids (and adults) are clearly on the spectrum, but don't really fit into any of the more common patterns, so they get the general diagnosis of PDD. That doesn't mean by itself that they are more or less impacted by autism. Just that their symptoms don't fall into one of the neat clusters of specific syndromes.
Read everything you can find about autism, and choose for your family what fits. There are many, many approaches and therapies out there. Most have "worked" for some kids, not so much for others. I put worked in quotes because it is a matter of opinion what the goal of therapeutic intervention might be. Some aim to cure autism. Some hope to change certain behaviors; to teach specific skills. Some intend to make life more pleasant for the kid and the family. My perception of autism as a developmental disorder has helped me to accept that YoungSon is developing in his own way, on his own schedule. It certainly doesn't mean that he is not developing at all, or that there are some built-in limits to where he will go. He has already far surpassed expectations that were set when he was diagnosed at 6 or 7.
When I learned to understand some of my YoungSon's more "autistic" traits, I found more patience, and stopped (mostly!) trying to change him. One example is his rigidity in thinking and planning. I am a pretty unstructured kind of gal, and it is nothing for me to spontaneously decide to go to the beach, or even just change the order of the errands I have planned for the afternoon. This just didn't work for YoungSon, although it was never a problem for my other kids. If I decided to stop for gas before getting to the grocery store as planned, that would throw off his entire day when he was younger. If the museum was too crowded, and we wanted to go to the zoo instead, he would melt down, big time. He has really gotten so much better about this sort of thing. These days, he is 16 now and doing great, although he seems to make plans before checking with me, and is upset if I can't give him a ride like he expected. Upset now looks like grumpy and surly, not major meltdown. This sounds much like normal teen stuff, not pathological. He seems to have outgrown most of the uncomfortable aspects of his autism. I give him full credit for figuring out how to get by in this mostly neurotypical world. He has friends, career plans, and a pretty typical 16 year old life. And he is still autistic, no question. Rigid thinking and planning is only one example of symptoms that were issues when he was younger, and mostly resolved, without disappearing.
I have pretty high expectations of all my kids in the realms of politeness, kindness and behavior in public. Some of YoungSon's behavior is a bit stiff and appears scripted, and he might mutter under his breath if he sees someone acting rudely - he has a hard time understanding why anyone would break these social rules. He sees life as black and white - good and evil, with no room for variance. But it he is pretty much able to handle himself in public, and I can trust him to take the bus to the mall, hang out with friends, and safely get back home. I never thought he would reach this stage. At 7, his IQ tested at 72, and I was told I would need to accept that he would never live independently. But now he is looking for a job! He will have to handle job interviews, and a whole new set of expectations.
No therapy plan, special diet, specialized classroom, or other formal, professional intervention really had much impact in our lives, although we tried many things over the years. His social anxiety ruled out most therapists. Schools in our area offered nothing that met his needs, so we homeschooled, until he chose to go back to public school, 2 years ago. He is doing fairly well, with no accommodations. My general approach was to structure his world to make him as comfortable and successful as possible. I don't mean to be suggesting anything so broad as "All therapy is useless; don't bother". I just want to put out there that even though we "failed" at most structured therapy, YoungSon is succeeding at real life. He is pretty amazing. Anything that that seems like a fit for your family, and is not too expensive, dangerous, or painful might be worth a try. But don't get too discouraged if you don't see the intended results, on a preplanned schedule.