I think I understand the idea - but why not just let users with no Steem Power upvote without reward? So the "upvote" number goes up by one, but the reward does not change at all.

Being able to "flag" in a less aggressive way (to reduce payout w/o suggesting the content is terrible) DOES sound pretty good to me. That one part I do like.

Without getting into implementation, that would indeed be the simplest version of this proposal if it were decided that no negative reactions (not counting flagging which would be treated differently) are desired and no positive reactions other than the upvote which exists today are desirable.

I worry that reactions reduce actual interaction by reducing the friction too much. A user might leave a comment, but instead they just hit "worthwhile" and move on.

That is interesting. Because I think without it we actually reduce interactions.

There are plenty of times I have seen posts on Steem that I absolutely do not agree with but raise somewhat interesting points that I think are worth bringing more attention to. If I have a lot to say on the topic and am in the mood, I will leave a comment (and likely leave a small upvote). But if I don't have much to say or at least not much to say at that moment (and if I leave it then I will likely not return to it later), I don't leave an upvote because I don't want others to mistake that as approval of the content. I can see how that could be seen as motivation to encourage me to just leave a comment, but we are all busy and lazy at times, so the reality is I would just likely skip it.

But if I had a Worthwhile reaction, I would almost surely click that since it is so easy. Now, if I had a lot to say and had the time at that moment to say it, I would still also leave a comment because a simple Worthwhile is not enough to express my full opinion. But not everyone has a lot to add all the time more than a simple reaction, and I don't think it is a good idea to put them in a situation where they feel the need to choose between not interacting at all or putting a spammy simple one or two word comment in the thread.

By the way, I upvoted your comment, but this is exactly the kind of comment to which I would give a Worthwhile reaction (along with a small reward with the slider) while intentionally avoiding to give an Approval reaction, had my proposal already been implemented.