>Perhaps we'd learn that nobody wants to change the 25% split, and it would be moot, however this alone would be useful data for further changes.

I think what we are going to learn is that most authors are willing to give a bigger share of the rewards to curator which is a good thing because higher rewards for curators means more engagement and more demand for steem power.
It is essential that every users knows exactly how the curation reward system works, most users don't even know that the more SP they have the more curation rewards they get. 
When users submit their vote they should be directed to a link explaining how the curation reward system works, educating users is key and I think that introducing curators/authors percentage will actually help in that regards.
I also think that authors should have the option to keep 100% of the rewards for themselves, the wider the spectrum the better. I agree entering a precise percentage is preferable because this will make every single post different and encourages curators to search for new content.

Really good point about the "free-market response". There's no better way to know how something will work out than to try it! That's also along the lines of what I was thinking about with SMTs. They will allow actually trying different curation strategies in live environments.

In the middle of writing this comment, I had a different, half-baked, idea of how to handle curation. Perhaps instead of paying out a % of the rewards from each post, there could be a separate reward fund specifically for curation. This way it would be possible, in theory, to get a larger curation reward for voting on a post than the author gets from the votes on that post.

The idea is to de-couple curation rewards and author rewards - i.e. not have them fighting for a share of the same pie.

As I said this is a half-baked idea - currently the "quality" of a post is determined by the value of the votes it gets, so this would require some other method of evaluating post quality, which may or may not be possible.

Anyway I think i'm rambling here - very glad that we're starting more discussion about this!