"We have seen that most comments hardly get enough upvotes to make a big difference, so I don't think reducing the reward contribution propagating from children is going to have that big of an impact.
They don't get enough upvotes because nobody wants to waste his voting power on comments but prefer posts! (and we can not blame them, I lost for example all my voting power just for upvoting responses on a single post today!That sucks!) In reality most would love to curate responses as well but they don't have the economic motivation with the current system!
The responses curation will be a problematic in future also if you not implement something like "seperate voting power" for posts/responses like suggested here... https://steemit.com/steemit-ideas/@liondani/separate-voting-power-for-post-and-responses