Does Solaris being alive, or not alive, sentient, or not sentient, make a big difference in your reading of the novel?

I don't think that it does to mine. While the Ocean is a main focus of the plot of the novel, the depth and weight of the narrative certainly lies on human interaction, human perception, our nature to define things with ourselves as the template.

Don't get me wrong, the answer to your question would certainly be interesting to know, especially to get at Lem's conceptual model. I think the story is more powerful in that we don't know.