Considering the wealth of western society I wonder if middle class saves less because it feels there is a safety net?
My guess is that humans don't have a particularly good sense of the future and as such, whatever amount of resources you will give to them, they will use up shortly. I think that's evidenced in each person's progressively larger use of energy or by comparing energy usage from one country to the next.
Whatever amount of stuff is easy enough to get, people will waste if they know they can get more within a reasonable time frame.
I bet you could do this experiment: Make a person live in a small-ish house and make another live in a big house. You'd probably find that the person living in the big house will accumulate stuff up until the point the large house is at a certain saturation point of fullness.
That's why you have people making 500k a year still bankrupt: They adjust their lifestyle to use up all of what they get immediately. You see this happen with lottery winners, pro athletes, stars etc. Since they get rich without knowing anything about money managment or discipline, their follow their natural instinct to scale their lives up in accordance to their perceived wealth, without making any calculations as to how sustainable it is long-term.
It might be sad but I believe that a society with no safety nets would make little difference and would just push more people to do desperate work once they inevitably fail to save up. Just watch documentaries on African countries and the likes and you quickly see that despite being dirt poor they still find many hours in the week to sing, dance, drink, smoke etc. instead of bettering their situation.
They have no safety net to speak of and are starving to death yet they have ample time to waste apparently. That's humans, we don't think years or months down the line, we think, like, DAYS ahead at best...
In a sense I think the middle class is middle class because they DON'T think about safety nets and don't want to end up depending on them, otherwise they wouldn't work so hard. It's just that after that day of work is over, they want to spend their money right away and let their future selves deal with the problems.