[cdgent]

Shouldn't the most successful cell be the one that does not expend excess energy by reproducing?

Think through this for a second - 'successful' or not, if a species didn't reproduce its not around anymore.

Reproduction is success, in biological terms.

[sig226]

I have thouhgt it through. What good does it do the original organism? Why does the organism care if it's species continues? Where did that come from?

Reproduction is success is an artificial definition that we impose on the biological system because of our own observations.