Why does economic growth or increases in real GDP such a good thing? Is it because unemployment generally goes down when GDP rises and spendingand...

Yes, that is pretty much
it.

The assumption is that it is better to have more money
rather than less.  When the Real GDP of a given country goes up, the people of the
country are more likely to be well off.  Unemployment generally goes down.  Economic
growth does not have to go along with a decrease in unemployment, but it usually does. 
When people have more money and when more people have jobs, people's lives are, for the
most part, better.

Economic growth just makes for happier,
less stressed people in general and that is a good thing.