I accept the Resurrection because believing that Jesus is the Son of God and died for our sins is one of the key parts of the Christian faith. It is in a much higher level of importance then the belief of God creating the world in 6 days. The Nicene creed sure doesn't mention the 6 day creation belief a necessity and the fact that most Christians don't take that interpretation of Genesis further shows that the idea of 24 hr 6 day creation is not needed for Christianity to be valid in the hearts of many.
I'm not getting your answer, yet. You're saying that denying the Resurrection has stronger consequences, but that doesn't speak to the logic of your argument. If he's using the same identical logic as you, then why is he wrong in denying one miracle, but you're right in denying another, regardless of which denial has more consequences. And I'll agree with you that denial of the Resurrection has stronger consequences.
Also I don't deny the belief that genesis is a history book simply because "science says so", but also because of Genesis itself. Part of that is references to ancient cosmology (especially the firmament) and other reasons. Various factors contribute me to believing that Genesis is more focused on teaching theology and other things instead of an emphasis on being historically correct.
Just out of curiosity, did you know that God actually named the firmament in Genesis 1? It's not really a mystery at all. "God called the firmament (raqiya') Heaven." Heaven is the firmament, and the firmament is heaven. And heaven (the sky), in numerous places all over the O.T. is described as an open expanse. In fact, clouds are said to be in the heavens, and clouds most certainly look like they're moving through an open expanse. IOWs, the Genesis account actually contradicts many ANE beliefs about the structure of the universe.
But forget all that for now. Because you're making the same argument, essentially.
You: The Creation account, read literally, is in conflict with modern science. Therefore, it must be figurative.
Bishop Spong: The Resurrection account, read literally, is in conflict with modern science. Therefore, it must be figurative.
Set aside, for a moment, the various interpretations of Genesis which may or may not contradict science. Because the Resurrection most certainly contradicts science. Spong and many other liberal theologians recognize this. What would you tell them about their approach to scripture? Should they put science aside, and trust the Resurrection account?