How do you find the sweet spot? The best way is to monitor statistics from your email blast software. See how many recipients open your emails, how many click a link, and how many unsubscribe. (Pay attention to the type of recipient, too, as your open rates for loyal customers will be different from new prospects.) Learn what works, make changes, and test again.
I’d rather not shift into being an email marketing therapist, but I’m not the first email marketer to have issues about being called a spammer. I, too, have been asked what I do in a social situation and had someone respond, “Oh, so you’re a spammer.” Of course, usually people are kidding when they call you a spammer, but but being labeled a spammer is one of an email marketers' biggest fears.