I've been following the mix-in-mono arguments too. While they are very logical, at the end of the day there seems no escaping that there are significant differences between mono and stereo mixing. You could do your head in trying to straddle both camps. Instead a lot of engineers talk about checking mono compatibility during their mixes. So they mix in stereo and check every so often that their work still sounds good in mono especially given that you can introduce weird phasing issues stereo to mono. There are plugins now that quickly convert the stereo buss to mono for an instant listen.

I like the idea that mono mixing can help you achieve frequency separation amongst instruments but as Bud says a lot of the main clashes are right down the centre anyway.