Title pretty much says it all.

What I have tried:

Modulated comb filters on two channels panned hard l-r where the filter frequency of each side is different.

Two similar but not the same initial synth patches (previous to processing) panned hard l-r and bused for processing.

Creating another layer that's higher than main synth that has haas or delay based widening then take all the center out and layer it back in with the original sound after some processing.

obvious ones: detune/unison/chorus/haas/delay standalone fx etc...

Does anyone have any more techniques to share? I would love to have more tricks 

And also more importantly do you think mono is really that important? Maybe someone who has played on a large variety of stages could let us know if mono really matters for live performance? I know it's still going to be occasionally encountered but how often really?

edit: let me rephrase: How important is it really that your mastered tracks sum to mono nicely vs losing power in when summed to mono? Do most clubs and festival settings really sum to mono these days or is that just older people regurgitating how it used to be?

Great question!  I always have my kick in mono. Also, mid-side EQ is a good technique. I use the haas effect on some layers and on some high hats, but sparingly. I also use the Logic directional mixer to make certain layers more mono. I also use that plugin for panning elements that are in stereo. I don't use the pan pot on the channel strip because it just turns down one side of the stereo signal and can change the sound.

  Reverb and delay are great for adding width too, as long as everything is well sculpted and mixed. I listen to professional tracks A LOT and I'm often surprised at the amount of hard left and right panning that is going on. In the end, I think that some sounds need to be more mono so that other sounds can sound wider. I once heard this line from a top level mixing engineer, "If everything is stereo, then everything will sound mono".

Cheers,
Rob

For mono compatibility and making sure the sounds remain relatively nice in mono, it usually helps a lot to create the wideness at source. If it's a synth, use unison or a wider layer to widen it up. If it's a vocal, double track or use a double tracking plugin like Waves Reel ADT or Revoice. If it's a drum, add another layer.

Also, wideness is above all about perception. If everything in your track is wide, then nothing is. Instead of trying to make your existing sounds wider, try narrowing the ones that don't need to be wide. It really does help. After you have some contrast between your elements, even just boosting wideness on something like the Ozone Imager on your master helps a ton.

I think you should have a healthy mix of mono and stereo. Most percussion and bass/sub should be mono and synths and effects/etc should be stereo. Main leads usually have a bigger stereo width. Next time you're in a nightclub listen to how the tracks sound, try and analyze the music and listen intently; pick out what is mono and what is stereo. Also it really helps to have a reference track when you're producing in which you can do the same thing with that.

It needs to sound good in mono as well. It can't lose all the synths. Look into phasing