Yes, you can enter this picture in the eligible gallery. The challenges make no restriction on the amount of post processing done. The feeling is that the voters will decide if you've gone too far with post processing.
Is it better than the one already there? That's very subjective. Some will say yes and others no. IMHO you've already got the better picture in the eligible gallery.
Now if you took this picture and increased the contrast of the upper level of the bridge and then applied the edges it might be better. I just don't like the way the lines fade out in the upper level. Others may have a different oppinion.