I voted ++ on your initial post, but that doesn't mean I agree. I don't see harm in your proposal, true enough, but neither do I expect any significant improvement from it. Maybe that's because I'm hardly interested in node reputations; I've pretty nearly never voted on a node just to be able to see its reputation, so eh..
The only argument that doesn't go either way in this context is that according to the pmdevils, the votes table is by far the table in the database. An unlimited abstain option may (or may not, natch) bloat it significantly more.
Makeshifts last the longest.