Um, I think you've confused my suggestion with someone else's. I agreed with them about it being an interesting idea but one that I didn't think would work due to the points that you also said. However, I answered so many replies I might well have accidentally agreed to the wrong thing by accident. Anyway, my position on requiring a post of comment to upvote or downvote is exactly the end as yours.
My suggestion was that up/down voting gave some sort of cost... Perhaps proportional to the amount of vests that would be allocated. However, this would mean that downvotes cost disproportionately more as there would not be any 'anti-curation' rewards. But I think that these actions shouldn't be effectively cost free.
Edit: Yup, definitely my fault! Apologies. I had answered without making myself clear. I think I had made those points (same as yours) in a different thread... Somewhere.