Trouble is as you said is alienating people by telling them that they are poor players who aren't good enough or some people are to good for the rest of the group.
Having a mix of Vets nights and Casual only can help. But you can end up dividing your customers or accidently telling people that they are rubbish if you say not to come to the vets night.
In general people will learn to avoid Timmy Power-Gamer because they are douches who will twist rules and work out power armies that become almost unbeatable. OR they just have the money to buy everything they could ever need and tailor their army to each opponent. They will also get the reputation as a WAAC player and wont get many games apart from against other WAAC players, or those who want to knock them off their high horses.
Having nights that you have low limit games can help as well. I know some people will still massively min-max for even a 500-750pts game, but in most cases people will get the idea.
Having Kill Team nights as well proved popular because even with the min-max players vs the casual ones you can have big upsets in the 200pts game.
You could if your boards allow it, modify the terrain to include more or less scenery. Knowing the players of the WAAC armies are all Tau for instance then throw up a load of high walls with siding doors for those nice melee armies to hide behind with no LOS from the enemy. Of course being able to open these doors to go through.
Or if they use a load of bikers start making tarpits or something to make them have to drive the long way around.
Some of the best ways to make the WAAC players get knocked down a peg or 2 is make up special missions of your own. Create stories and scenarios that have weird objectives that the min-maxers might not be suited towards, but your average army will be.