A:It is true the Magen David and six-pointed stars in general, have been used in mystical practices.  So have crosses, for that matter, so I wouldn't be troubled about it.  It is probably precisely because of their association with the people of God that misguided and superstitious people have attempted to abuse them for magical purposes. Even the Lord's Prayer has been invoked (by reciting it backwards) in an attempt to place curses, but I wouldn't cut it out of my Bible on that account.

As for the story about Solomon (which I have heard before), I suspect it is apocryphal.  According to a book from the Jewish Agency, the first known use of the star by a Jew dates from the seventh century BCE, well after Solomon's time.  This indicates there is no historical or archeological evidence that Solomon ever saw it.

Even if a similar symbol did happen to have been associated with cultic practices in ancient times, the important thing is how it is understood today.  The symbol is now widely recognized and associated with Judaism and the Jewish people, and only a small majority would understand it to mean anything else.  Just as I would not wear a swastika here and now because it has had positive associations in other cultures in the past (ancient China, for example, or the Navajo nation), I would not avoid a Magen David just because it had negative associations in other cultures in the past.  Am I making any sense?  The symbols are only symbols, and the statement they make depends on the cultural surrounding.  If you find yourself among people who genuinely associate the Magen David with something other than what it means to you, and they are offended by it, then by the principle of I Corinthians 10 you should avoid it for their sake.  Otherwise, I wouldn't worry about it.