I strongly believe that he's better off spending that money elsewhere unless he didn't already.
The GPU is the most important factor to rendering and unless the next GPU costs more than 200 dollars more he'll be better off upgrading that.
Heck, I have great rendering results with an I3 540 when using my HD 6850 to render, It takes me about 60% of the length of the video to render it at 720p, and that's when using an old low end CPU and a mid end GPU.
By the way, if you're using Sony vegas get an AMD gpu, Sony vegas pro 12 supports them perfectly and they render very quickly.
Also with the new AMD technology games should be able to take advantage to extra cores, Starting with a big name "Battlefield 4" which will get a patch a few months down it's lifecycle to support Mantle.