I passed up Iron Maiden for Night Ranger in 1984 or so! I enjoyed the Night Ranger show, but it would have been cool to see Maiden - it was the Powerslave tour - never seen them live, but I just wasn't as into them at that point.
I wanted to see Ozzy - it was the Bark at the Moon tour - but my dad wouldn't let me go, because we would have just gotten back to Japan from a trip back to the States - Night Ranger was Japan too, the NHK Hall in Tokyo.
Another one I blew off - Kazumi Watanabe, with Jeff Berlin on bass and Bill Bruford on drums - but it came out on DVD recently, so I've kind of seen it now...
I think my favorite show in Japan that I did see was Deep Purple in 1985 on the Perfect Strangers tour - "Destiny Brought Them Together Again!" (Or so read the t-shirt)
I wish I had seen Stevie Ray Vaughan and/or Frank Zappa, but never had the opportunity...