Wolf, I am with you. I say good shabbos to everyone. if they answer me, they answer me if not, not. Hevei makdim kal adam b’sholom.
Lavdavka, I think you have a problem, I am not sure what it is or why you feel the way you do. Most people who are new to a shul, would be DELIGHTED to have people take notice and say hello to them. Do you feel uncomfortable when noticed, like all eyes are on you, making you self-conscious? Then you should not go into any shul other than the tried and true one where you feel familiar. But know this: MOST friendly people WILL say good Shabbos to you. There is no hidden agenda. they are simply being menschen. The proper response is GOOD SHABBOS, said with a smile.
it’s liek giving a woman a compliment on her new dress and having her respond, “Oh, THIS old thing???” Inappropriate reaction to something nice. A simple thank you will do.