I think if you have all the things in life that money can't buy, great family/friends/relationship then you are much happier than people who are rich that don't have those things...
BUT, worrying about money and not having the money to do things you want certainly causes unhappiness. I've always had a great life, a fantastic husband and a loving family, but I worked in a job I hated for years because I couldn't find anything else, because I needed the money, and it made me very unhappy, and I couldn't enjoy the amazing things in my life.
A few years later, my husband (then boyfriend) and I had saved enough money to travel the world, and I was the happiest I'd ever been in my life, but you can't do things like that without money.
Now that we have our baby girl, we feel like our lives are perfect, and the only thing that would make us happier is to have more money. I'll have to go back to work after my mat leave ends which breaks my heart, but we have bills to pay and need to pay for the roof over our heads. If we had more money then we would have absolutely no worries, and therefore be happier.
It depends what makes you happy I suppose, for me to be the happiest I could be, the only thing I would change would be the ability to not have to leave my daughter to go to work, and travel is the biggest thing that makes me happy, I'd love to be able to take her to so many places around the world, I want her to have experiences, and without money we can't do that.