+1 for "be flexible."
Well, I think you're on the right track -- if people are getting annoyed that you beat them all the time then I think the approach is to offer them advice. If they don't want to take it then there's really not much else you can do. They seem to still want to play, so if they want to compete with you they'll have to get better somehow.
I'm sort of starting a similar thing in my area where I have a semi-regular Dominion event. Granted, it's part of another board game night so other things are going on, but it's been doing well so far. I'd like to have people get much better at Dominion, but that isn't my main goal (the main goal is just to keep a continuing interest so that I can have regular tournaments).
I hope this isn't the case, but it may be that they don't want to play competitively. I hope that isn't the case, but if you find things that are making people fall in love with the game, certainly let me know. My second session of this is tonight so if I get any gems, I'll share them :-)