I think if you define Mustachianism strictly as a financial approach, not only do you run the risk of becoming a miser, but you've missed a large part of what this guy is trying to teach people.
I care a lot about the humanitarian issues stemming from our current overconsumption and environmental degradation. In practice, this means that I not only look for the money-saving solution that also reduces resource usage, but often deliberately choose to spend more money if it means lower resource consumption. Early LED adopter, early EV driver (though the car will literally pay for itself in time, the up-front cost did reduce investments), etc. Going farther to trading my own money for others' resource efficiency, I even offer two free public chargers (at our home and one rental) to increase freedom of movement for fellow drivers in an EVSE-sparse area. With a "same boat" mentality, this can be framed as uber-Mustachian, but it does cost me money and I personally get nothing for it, so take it as you like.
As far as deliberate anti-Mustachianism... I indulge occasionally. I have a friend who's an artist and I catered his latest opening on my own dime - my way of supporting the scene without adding to the stack of pictures I can't hang because we gave up 40% of our square footage to live efficiently.
I also seem to vacillate between minimal Christmas spending and actively encouraging my sisters and their kids to give me long lists of shit so I can blow $1000 on presents. I felt deprived as a kid and was stuck in overcorrect mode for years - so even when I don't want anything, I get a huge rush from indulging them.