I doubt I'd really notice, except maybe as an afterthought. But if it isn't important to either your plot or characters, then it probably doesn't matter. Religion, in terms of believing in a higher power, I think is only important to the extent that it affects your characters and plot (I mean, if you've got a rabid priest making trouble for your characters, then yeah, you may want to expand on that a bit.

In terms of religion as Something the characters strongly believe in (like a rock musician saying that rock n' roll in his religion), then, yes, I think it's extremely important as their driving force. But that's metaphorical, and not what you're talking about here, right?

It sounds to me like you've got plenty of other forces in your society (species and nation as stratifying points) that can replace higher-power religion quite easily, and provide the driving forces in your world.

I think ailelie covered everything else I would say, so I'll leave it at that. ^_^