I don't know whether you should upgrade by abandoning ship, however I can tell you about my experience from doing the same thing.
I had a stock clocked FX-8350 and I moved to an i7 4790K. It's faster but nowhere near to the extreme levels some here will say. In actual fact, I was disappointed because I naively began to believe some of the things people spout here (When so many people keep saying the same thing, you sometimes start to think there must be something to it). In some areas it's a very noticeable difference but in others it's marginal at best.
As some have said, the FX-8350 is without a doubt faster, and smoother in actual use than the FX-6350. Having used both, I can at least attest to that from my experience.
So all in all, it's a matter of economics. If you can, and you don't mind spending the money? Then do it, it is an upgrade, but try to have realistic expectations otherwise you might come off a little disappointed.
Very well put and full of honest simple accuracy.