I have to disagree again. My disposable income, as you define it, has risen and fallen in my retirement years, even though my expenses have been rather stable. But my standard of living has not changed as my disposable income has risen and fallen. I have had expenses of about $2,000 a month with retirement income of sometimes $2,500 or $3,000 or $3,500 a month. With my expenses stable, the added disposable income had zero effect on my standard of living. All I did was to plow any excess income back into my portfolio.
Having that cushion in my budget allows me to go on small spending sprees now and then without having to worry about busting my budget. That's a good thing, of course, and it allows me to maintain the standard of living I had before I retired. But that cushion ranging from a decent size to a huge size makes no difference to my day-to-day lifestyle.