Define "worth it" If you are replacing cpu and motherboard anyway, Intel becomes more attractive price wise, at least for a non - K ( locked) cpu with a decent but not great motherboard.
Say within $100 ish compared to a 6300/990FX motherboard. If you are dropping a 6300 in to a AM3+ mobo you already have, "worth it" becomes a $200-$300 difference in cost. At least. Which would buy you a pretty darn good video card.
I upgraded my PC one step at a time over the course of a year and a half. closer to two years. Staying AMD meant I could change one part at a time, never spending more than $200 at one time, excepting my splurge for the 290X, and just install the parts as I got them. Getting noticeable improvements as I went.
From.... X250 dual core budget box with craptastic mobo, to 975BE, just dropped it in, bought a new case, one month, the Sabertooth board the next month, swapped everything over, added more psu a couple months later, then a 7870 OC video card, used it that way for almost a year.
Bought high quality ram in the middle there somewhere.
Then the 8350, again $200 ish, a period of saving, and took the plunge on my R290x.
And never stopped using it to game for longer than it took to install the parts. Intel's habit of changing cpu sockets more often than I change my underwear would mean this type of long term low budget approach to a pretty high performing gaming rig would mean no forward/backward compatibility.
So your "worth it" may vary greatly from other people's "worth it" Especially when you take in to account that a motherboard swap, which comes along with every Intel cpu upgrade/socket change, means a new copy of Windows added to the cost, at least for most people.
On the other hand, if you are building a system from scratch with a budget of $800 ish or greater, Intel breaks over the price/performance curve and becomes the way to go, although it means using one of the lowest end cpu's. At $1000 or greater of total system budget, Intel takes a decisive lead and never looks back.
I have been an AMD fan for a long time, and in real world gaming performance I am extremely happy with my mildly clocked eight core chip.
Like everything else in life "worth it" is a moving target that only you can decide for your own situation.
But no way in heck would I build a new PC with less than four cores. Real cores, not two hyperthreaded ones.