Whether the IS will improve your photos is hard to say. Your 500 px has some pretty nice work on it already!
What I appreciate about IS a lot is its ability to steady what I see through the viewfinder. Even without a definitive improvement to an image, it makes composing the image quite a bit easier (for me). If your subject is moving, IS will not help in darker (e.g. cloudy days) environments. For that, you need to up the ISO or choose a larger aperture.
Thank you so much your shots are very impressive! My 500px are mainly shots taken with my 60mm f/2.8 Macro with IS. I'm going to give the 70-200 f/4 IS a try and see if indeed I get better quality, stick with my f/2.8 and flash for night. Thanks for your help I appreciate it.





