For tier-specific tourneys, title them as such: "Tour Pros Only!!!!" instead of "Weekend at St. Andy's" or whatever; if you have 1 for each tier, you should have far fewer problems.
If you are awarding prizes (always a good way to drum up interest, even if it's only 10 cr. balls) award them no matter who's on the leaderboard. In other words, a Legend may have the lowest score, but the lowest-scoring Amateur gets the prize. Post a message in the forum: "Everyone is free to play, but only x players are competing for the prize."
You can also devise a handicap system. This takes a lot of work but is great for newer players.
Right now our cc is doing a lot of team events, where legends, TM, and master or below, 1 of each on each team, compete together with combined scores.
Although the player on top of the leaderboard gets a WGT trophy, you can award your own virtual trophies and medals... there are (free) Web sites where you can "engrave" them; or you can do it yourself with a photo and a graphics program.... post them on players' walls.