The post I made was very early, many things have changed since then.
I have an alt account which I use to post my actifit results.
Why am I telling you this? Because the alt has the 15 SP from Steemit, nothing else. And the RCs, ever since the 10x adjustment to them is always at 100% (but my usage of the account is limited).
After checking on Steemd, it tells me it's enough for 19 comments or 100+ votes or 100+ transfers/powerups. I believe it was said the RCs necessary for a post and comment are the same.
Of course, that would deplete my entire RC bank and 5 days are needed to be filled. Probably per day would be 19 / 5 = almost 4 comments. That's 3 comments per day and a post every other day or something like that.
If they are well thought-out comments 3 are not so few. And, because they are good comments they have a good chance of getting upvoted considerably. If the rewards are powered up, in time they'll have more RCs. And that's without the investment option.
There is, of course the possibility that they comment more in some days, and less in others, to let the RCs regenerate.
If newcommers would have a 25 or 50 hard cap on comments, apart from the spam, many will feel the need to consume them, and leave unworthy comments, that would not only not bring value to Steem, they wouldn't help them either, despite the higher volume.
Sometimes scarcity helps, because you treat your available resources with consideration, you don't just start using them without judgement.