Much simpler to compare billionaires to hoarders/morbidly obese.
I'm sure you personally get more happiness by not doing (too much) more than necessary, but as a "Christian and humanist", aren't you asked to do more?
You can replace "being rich" with "helping others", it still applies: you can trade comfort, sanity and health for more output, whether that's money in your account or helping those in need.
No. I'm a Christian and humanist you insensitive clod :)
Really and sincerely I do not.
If there's one philosophy I could share - that's given me a truly awesome life filled with gratitude, meaning, mostly decent health, intimate human relationships and personal agency it would be look for the riches you already have.