I think an underlying concept, not directly written out in the story but brought up by your question, is the importance of obedience to God. Adam and Eve didn't necessarily have to know about good and evil beforehand, but their lack of obedience landed them in the position they found themselves. As to whether how central that theme should be, I think that's up to individual interpretation. I don't know if eating from the tree of life has as strong of an implication as you say. If it means that they'd live forever in the physical world, that just means they live forever. They're still subject to physical limitations and the will of God as a creator. If anything, I could see it as an even greater punishment, as it forces them to live forever in the physical world (which God has now allowed to cause them to suffer) meaning they can never be released from life and ascend to heaven.