If you read Terry Pratchett, he will explain, quite convincingly I think, that gods derive muscle, clout and lnfluence from having believers. One of my favourite TP books is Small Gods, for which this is a central point :)
The other image that comes persistently to mind when asking what god gets out of all this devotional behaviour is a scene from the Peter Cooke / Dudley Moore version of "Bedazzled" I think it was - Dud asks the same question of Peters Cookes Lucifer - So PC illustrates his point by asking Dud to participate in an imaginary example. Peter Cooke sits atop a red post box and says I am god - worship me - so Dud prances around the pillar box a-singing and a-praying to Cooke for a few minutes, then gets bored and asks Peter Cooke if he could have a go - and Peter, as Lucifer, says - thats just what I said, and look what happened to me! :)