Isn't money just the middle man?

[BCHS]

I've been studying economics for a relative while now (Highschool and university) it is an extremely intuitive system though fundamentally GDP just seems halfway there on the logic. No one is getting money for the sake of money (excluding inherently evil game of exchange markets. People want to make money so they can spend it on things that they believe will make them happy. Thus people are just trying to be happy.
Couldn't we deal with growing materialism and social problems by replacing GDP with a measure of happiness, or more technically a measure of life satisfaction?

[Bored Gremlin]

We would replace GDP with a measure of happiness if we could. But there is no objective way to measure happiness. Surveys are subjective and not comparable across countries and cultures. Measuring endorphine levels is expensive and too narrow.

[Tommy L]

Yes money is a middle man, a way to barter, a way to measure through prices. It in itself is not wealth, thing about it are fiat money is really green toilet paper. The fact that we have value to it is what makes it good in barter. Adam Smith wrote his book to make that distinction.

[Spotty J]

Why speak of "replacing" anything? GDP is not a measure of money, it's a measure of real economic output. There is a need to know that info, regardless of anyone's happiness. No one claims that GDP tells you how happy anyone is, or is a measure of a nation's spiritual well-being (whatever). GDP is what it is -- a measure of economic output. No one claims otherwise.

The only people I ever see who don't seem to understand what GDP is, are the people who criticize it for not being something else.

If you want to create your own measure of happiness, you're free to do that. Then you can persuade other people to pay attention to your measure. However that's a hopeless cause because you cannot measure happiness in any object consistent way. One reason economists use the metrics they use is that they can be counted and measured. No point in having a yardstick for some immeasurable quality.