We have a choice to buy Steem and/or to earn it.
It's actually not a choice whether we earn Steem or not - since it's not mainly in our own hands to decide on how much we get from the cake, unless we upvote our own content :-)
Many factors have an influence on the distribution of rewards, such as timing e.g. What's definitely in our hands is the distribution of power that leads to distribution of rewards in the end - so there is our regulating screw!
According to the Steem white paper invested time and invested money are equally valuable. Well at least it's written in the papers...
perhaps I should have said "try" to earn it by providing good content, but you have a good point. I actually think time is more valuable myself, it is more limited, as we don't know how long we have to live our lives