1. Your sigs do not have to be so big, i go 400x125 max
2. too many pictures, because the size of the sig
3. You have to work on text, it really brings down the sig when it is almost a quarter of the sig is text
4. Try some brushing, with fill layers for a background, or some lighting effects
5. something needs to be done with the pictures, have a main picture, not a bunch of pictures.
I am not at all a professional, but thats what i saw that you could work on. Remember, the larger the sig, the more space to fill, the worse it looks.