I think you are exactly right when you say that uncertainty about lifetime income prevents optimal spending habits. It just doesn't feel safe to spend beyond your means when there is no guarantee of future income.
In general, there are two counterbalancing factors. One is that high spending has high rewards and is often more manageable than people expect. The other factor is that saving leads to non-linear returns (such as compound interest) which can eventually have a significantly bigger net impact than the original money.
