In the first, the wire box frames and makes the picture for me, without it the frame extends forever and will make the girl infinitely small and seemingly insignificant. I disagree very strongly and feel it is essential. It adds context and provides a "school yard feel". IMO, the first is perfect.
In the second however the conduit is too significant, and is definitely distracting. The pose looses a sense of shyness, and as such you loose the Valentine message; it becomes just a girl with balloons.
The last is ok, but the crop bothers me. I don't know if it would work otherwise. The bokeh is also distracting, not that it's "bad" in other situations but with these contrasting colors it's not working for me. The concept is also a bit too cliche for my taste.