Seems a bit circular to me. If the most important thing a human can do is bring life, then that life also has as its most important mission to bring some more life into the mix and so on. You end up with an endless chain of causation and no real answer as to what makes the entire thing worthwhile.
I'm pretty sure reproduction/biological success is considered the prime biological directive of any species. There's no romantic explanation for it be worthwhile.
I'd say the idea of a directive is also a romantic explanation, since it implies a some sort of planning. The reality is more tautological. The current crop of beings is there... because they made it to this point. There is no deeper reason or value to be assigned to their survival.
A being doesn't want to reproduce in itself, it wants to fulfill needs that compel it to reproduce. A desire for sex, for companionship, for a social role, etc. It's possible to be highly attracted to someone who is infertile because we chase the signs of procreation rather than its actual occurrence. We can rationally plan to make procreation happen but even in this case it is an illusion, we are still chasing some state of mind that leads to procreation.
On the contrary, I am trying to dispel the romanticism here and the hidden additional romantic layer that anthropomorphizes the process of evolution itself by giving it some sort of direction.
"An endless chain of causation" isn't circular, that's more or less the definition of life. What's the alternative, a task that a species must complete so that it can then go extinct?
Perhaps a chain of loop-de-loops would be a better mental image: a series of circles rather than just the one. If the importance of any life is justified by its relation to other lives that are themselves justified by other lives, you end up with no core importance. There's no meat inside the loops.
I don't have a definite answer to your question but looking at most of what has happened in history I do wonder if developing opposable thumbs and a frontal cortex was worth it.
