I'm not a particularly good songwriter, and in fact I haven't let any of this forum in on the pop stuff I write, but here's how I approach writing lyrics. Find the emotional center of whatever story or idea you're trying to express, and choose the words that best and most honestly express that. Personally, I don't really think much about how revealing the words are. I would say write in any details that enhance or clarify the emotional impact of what you're trying to convey, and leave out anything that doesn't seem relevant to your point.
I don't think there's really anything you can do to stop some people from speculating over the meaning of your songs. Ultimately, I think it's best not to worry about what others will think, and just be as honest to your thoughts and feelings as you can. If there's anything you really feel you need to keep a secret, there's no need to expose it in a song until you're ready to share it.
I hope that's helpful in some way.