In my opinion, yes, the existence of God, or any 'higher being' does matter.
It may not have mattered all those years ago when we were supposedly less developed as human beings, but as time went by, and ideologies and theories shaped our nations, continents and the world as a whole, religion has become an important aspect in life. This is, unfortunately, whether you like it or not. Some countries are still governed by religious beliefs, whereas some have changed to democracies, and in some few cases, communism.
I digress, however. If people have a notion of a God to believe in, then for them, it feels like they have a means to an end. Most people, that are religious, will say they are on this Earth to do their duty for their God. Others will speak of money, cars and a family. However, these two separate kinds of people live in the same societies. Therefore, each is affected by the other. We as human beings have learnt (for the most part) to be tolerant. Most of us will not expect a man to be fired from his workplace for believing in a God. Just as it is vice verse.
The existence of a God DOES matter, but only to the person or people who believe in it. Other people are affected by the notion of there being a God too, but to a lesser extent. Tolerance and acceptance are the main values that are needed for a society to work, and if people can't be tolerant or accepting of another's view, then society will disintegrate.
Therefore, it is important to acknowledge beliefs of others that there is a God. Which is why the existence of God DOES essentially matter.
