I've been into Parelli for years and am playing in Level 3 right now. It's amazing! Parelli can take you from very beginner to very advanced. And believe it or not, you CAN show and be successful in the show world and do Parelli at the same time ;) Some people don't believe that, but I have a lot of examples I could point out.
Anyway, I think you should go for it! You and your horse will love and benefit from it. As to answer your question about the porcupine game, no, your horse won't move if you simply pet him. When you teach the porcupine game, you always give the horse a warning look first and your body language is intense. When you simply pet your horse, your energy is down and very soft, so that alone will be all the difference your horse needs to tell whether he should move or not. When you come out of your relaxed position that's when he should pay attention and figure out what you want.
I, too, know the "looks" people give others when doing Parelli. It's ridiculous really. I mean, don't they have anything better to do? I just ignore it. I don't need to prove anything to anybody. The proof is in the pudding, after all, and I don't speak a word about Parelli, I simply let my actions and my horse's behavior tell the story. THAT'S how you be a good example, not by trying to shove things down people's throats. I care about what my horse thinks of me, not what others think of me.