|We all get the urge to buy a new lens once in a while, and it seems as though we forget about what makes a great picture. When it is all said and done, composition, exposure, and subject are the real call when it comes to successful photography. I took a look at your portfolio and saw a lot of great shots taken with what you have now, and I also see a lot of superb pictures taken with lesser equipment than we have.
My suggestion is take a real good look at what you feel you need but don't forget the basic needs of a good photo.
Oh, by the way Sigma makes some great lenses that will give most of us amateurs all we ever needed in a lens, and at a lot less than the fabled "L" glass.