It could also be that the polepiece underneath the G is higher in resepect to the others. If this is the case just lower it a little.
A guitar gives you so much to customise its sound, anything is possible really.
As for the reason of wound-and unwound G strings I used the think that the reason for the unwound G's was related to players desire to get more ring from their strings, maybe also related to style of music.
You could easily interchange a wound or unwound G and see what you think about the sound. Maybe experiment with different gauges as well, as this will drastically alter your sound too.
I've been trying out new slinky sets and have noticed that none come with a wound G. I have four different sets in front of me that I am thinking about cannibalizing for a custom set. But I don't know if I want to sacrifice four sets for the sake of one..... Maybe I'll pick up some single strings online instead.
I use D'Addario Chromes .010 - .048 on my guitars. Their flatwound, so they sound warmer than usual rounds. My G string is wound, but I've already tried using an plain string (same gauge as normal) and it works quite well.