One of the premises you mention is that the creator (if there was one) had some specific purpose for its creations, just as a builder has a purpose for the house he builds. But, what if the creation was just a way for the creator to express himself? An artist might produce art without purpose, right?
As for the meaning of life, I think the Monty Pythons' version has it all covered! :)
We are in total agreement about Monty Python. :) As for artists without purpose, I'm not sold. Their want/need to express is their purpose (as is, I think, their want to connect with others). Just because their purpose does not necessarily have a practical value, doesn't mean the purpose is absent. God as artist could just be some dude creating his own captive audience, and worship or "love" may be his/her/its only purpose.
I guess my point here is that God's purpose doesn't matter at a basic level. It doesn't change that an individual's fundamental purpose and value is him- or herself.