If one invests the money correctly, they would be happier. I would use the $20M dollars to re-enforce the four items which would make me happier.
Money might not buy you happiness. But it can sure as hell rent it. Seriously I would be pretty darn happy with $20M. I am already kinda happy but I could be a little bit happier. I am 60 and I figure I probably won't live much past 90. I would spend $500k fixing up my boat, $2M on a house with deep water access and no zoning issues, keep $100k to day trade just cause it is fun, swing trade and invest the rest, and probably just help folks who need help and actually CAN be helped, with maybe half the income. I can live just fine on $60k/year once boat and housing expenses are down to just simple upkeep. Catch a few crabs, some fish, a few shrimp, tong some oysters, trap some crawfish, get me a gator every season and maybe a turkey and a goose and some ducks, basically kill and eat anything with a face on it that doesn't answer me when I say hello or that barks or meows. One must have standards, after all. Car? The one I got was given to me on the condition that I could get it started and drive it home. I will drive it til the wheels fall off. So far they don't even rattle very much. Clothes? Overalls and tshirts. And socks. And boots or sneaks. Ball caps. That's it. Closed casket funeral cause I don't have a suit. But having the boat and a new house/workshop/office set up just so, would indeed make me happy. Of course the main thing would be having my old lady who is the best thing since sliced bread, but even if I was single I would be pretty happy with just those things. Everything above and beyond that is just gravy. If I had nothing at all I would still be kinda happy cause life has been good to me and I have on occasion felt the joy of returning the favor, but not as happy as I could be with that hypothetical $20M. If I get to be a good trader I might well earn a couple Mill before I hang it up, and that beats a kick in the ass, but $20M, even $10M, would be very nice.
Iron and Growley. Strong relationships according to this incredible Harvard study (75 years in the making ) is a huge key to Happiness.
As I use to say, happiness is a state of mind. It's also a temporary cursorial feeling, you don't walk around happy all the time. Money it self does not make you happy, it's just a tool, like a screwdriver. You don't become happy by staring at the digits on your bank statement. It's what you do with the money that make you happy. Things like personal freedom, the ability to follow your own will without things holding you back, go where you want, stay as long as you want, do what you want. Family and friends are of course important, we are social creatures and we need other people around us. A least the majority of us.
I've been told that people who are diagnosed with terminal illness are grateful for having given another day to live. Why so many people take things for granted is beyond me.