The half-point idea is an interesting one. I find it hard to think of genuinely good reasons for wanting to know how positive a score is before deciding whether to vote up or not, and I haven't heard any good explanations from anybody else yet either. That's to be contrasted with the multitude of bad reasons for wanting to know the score beforehand, which exploit common cognitive biases that we are all at least partially subject to. I do find the idea a bit heavy-handed, but I think it would make the community slightly less herd-like and a bit more rational.

Of course, you'd also have to change the code base so that once an initial blind vote has been made, any further changes would only register at the lower value.

As to whether it's unfair, you could explain it as getting an EXTRA half point for your willingness to make a small sacrifice for the betterment of the community at large. You could even make it 1 point versus 1.5 points.