Hello!
I have made a couple force directed graphs using d3.js in the past, some of which I believe have the same fade on hover that you describe. Therefore, I believe It should be easy and quick for me to implement into your file. I set my bid to 3 days, but that is mainly to allow time for any additional communication in case it is needed; I could have the modified script done and ready in 1 day for your review.
My changes to the script would be to add one new function for the fade in/fade out effect. The body of the function would be about 7 or so lines. I would also need to add several lines into the existing body of the script as well as some lines into the CSS for the smooth fading transition, though if you prefer, I can do the CSS portion in-line. I will add a comment above each of my additions explaining what it does.
Thanks for your consideration,
Andrew Alar