I'm always impressed by attempts to empirically answer questions which typically receive less rigorous research, and the log-relationship and plateau of income vs happiness both bear out my personal experience.

However, I specifically asked about retirement because it shares some interesting characteristics with your supported findings.

A) Retirement accounts are intangible. I may receive pleasure and happiness from imagining the money I have in them, but believe it would be a hard case to make that I received true happiness from increasing them

B) Enabling retirement would seem to dovetail with the plateau effect. To wit, if I make $40k now, but am unable to save enough to make $40k in retirement, my happiness would plummet if I ever retired. If I make $60k now and save enough to provide $40k worth of retirement income, then my happiness would be substantially improved. Therefore that +$20k has a secondary effect of making me much happier later in life

I doubt it would change the findings, but if true, might shift the numbers a bit.