I definitely agree that commenting is the key to building the value of a Steemit account over time. At the outset, original blog posts sent out into the ether are unlikely to gain much attention, so the key to growing a new Steemit account (and following) is with comments. Sort of a grind at first, but it can become enjoyable if you follow the right people. :)
That being said, a newbie Steemian starts with 15 SP. As a result, due to the way the Steemit curation algorithm works, there is a very different economic result for someone commenting with 15 SP vs. someone commenting with 15,000 SP.
My account just hit the 30-day mark over the weekend, and I am now re-adjusting my strategy. Curation awards (i.e. comments) are much more powerful (potentially exponential in nature, as you have suggested before) the higher your SP. So I am not focusing as much on the $$$ payouts right now and focusing much more on building my SP on an exponential basis. From 15 SP to 150 SP, and from 150 SP to 1500 SP, and then from 1500 SP to 15000 SP.
Comments are not curation...curation is curation.
Getting an upvote on a comment is an author reward and that has nothing to do with your SP. If I upvote a comment or an article, the vote counts the same for the person (as long as the voting percentage is the same).
This strategy is for newer people. Curating is something that is not a great deal for anyone under 50K SP. Even the 15K you mentioned doesnt net a great deal in proportion.