To me the real question is exactly how you define quality of life.  If having a high quality of life is defined as owning lots of stuff, then yes, you could say that the quality of life would be lowered.  In some sense this is part of the reason that past attempts to get people to conserve energy have failed - you are implicitly asking people to make a sacrifice in their lives - to give up something that they value.  The problem is that they still watch the advertising, and still want the stuff, and they don't like the fact that they cannot have it.

There are of course some things that we really truly need to survive.  Food, water, shelter, clothing are the basics needed just to keep the body alive - things like companionship and friendship would be needed by most people.

When energy prices go up, and people will have to go without, they will still remember and miss the things that they used to own and the things they used to do, and they would resent the fact that this is no longer possible.  People would be inclined to reach for anything to keep things going so that they don't have to give up their material things.

My thinking is that there needs to be a fundamental shift in thinking so that quality of life is measured in entirely different ways.  If we can reach a point where many of the materialistic and consumeristic urges are gone from our lives, then giving up material things up is no longer a hardship.  In fact, it can be liberating in the sense that having stuff that you no longer want or need is a nuisance.

Such a change does run against human nature to a degree, but I believe that many of the wants and desires are planted in our minds by the media.  For that matter, I doubt that most people could make such a change overnight - it will take a while to unlearn consumerism.

A non-materialistic society would seem to be incompatible with a capitalistic society.  Right now with growth being an economic requirement, there is almost a need for people to buy more crap each and every year in order to keep the whole thing humming along.  I have seen other comments here where people suggest that a new economic paradigm is needed - the problem is that nobody really knows quite what it is going to look like.