More capricious God needed for supplication?

Often I wonder when we/I offer prayers of supplication, what's the point? Sure, it seems reasonable at first glance to ask the most powerful entity in the universe to grant me/us special favors, but I also have a hard time thinking that prayer alters God's desire in any way. Now of course I believe in free willed synergy, which means that prayers such as the Lord's Prayer come relatively naturally. Also, I very much enjoy singing Psalms about what a hoss God is. So, I'm not talking about praising God or asking like Jesus in the garden or Mary when pregnate, for the strength to do his will. Those are great prayers. For some reason asking God for STUFF or outcomes seems a little silly.

Today chanting the 24 stichera (painful for my ever-sore sick throat) I remembered yet again that in the Old Testament God is rarely presented as a monolithic and steady guy. Rather, we see that God frequently changes his mind, acting on behalf of those who do his will, using them as vessels, and turning a vengeful countenance towards those who harm them.

I guess that I fall into the typical theologian's trap of thinking that I know God and that really... well really he's a sweatheart. In fact, attributing the lovey dovey words to God that we often do is a bit of a trap. It forces God into our boxes of goodness and steadiness. Perhaps a more capricious God is necessary for our supplications to make sense. Indeed, our services use plenty of non-cuddly and plenty of changeable images of God. One hymn today was something like "God of vengence show yourself" (though I don't remember the precise wording). I get the feeling that generally speaking our ancestors didn't have quite the unearthly view of divinity that we tend to fall into. They could ask God for things and results, sometimes God answered and sometimes not, and they were content that God's ways were not our ways.