So I guess to fine tune the question, does nage's feeling they get from spreading fingers negate/outweigh the danger of breaking them? You may have to speed up your training to find out.
Hmm, does the feeling that you get from wearing a hakama and training barefoot outweigh the danger of tripping on it in a fight or stubbing your toe on asphalt?
There are just so many training things that don't translate well to a fighting situation that this doesn't rise that high on my list of things to worry about.
I'm not sure about actively trying to push the fingers out, but I think that if you do things a certain way the fingers will tend to end up in that position, and that you can then work on getting the same thing to happen without that obvious outward expression. OTOH, I think that it will be harder to do certain things without working through that obvious outward expression.