I have the ATV 3 and it's a great device but Apple may drop a new ATV this year.
I've been wanting to get an ATV 3 back early last year, but then I waited until WWDC to see if a new version would be announced...
Then I waited until the iPhone 5S announce date to see if a new ATV was also announced....
Then I waited until the October event to see if a new ATV would be announced...
See a pattern here?
A new version has been rumored to be 'just around the corner' for a good year. I went ahead and purchased an ATV just a couple weeks ago. If they finally do announce a new one this year, then at least I'll have been able to enjoy this one for a while. And chances are the then 'old' ATV 3 will probably be updated to the same OS as whatever new one comes out and have most of its capabilities. And when I do decide to upgrade, I'll only be out $100 for the ATV 3, so it won't be that big of a loss.
Waiting to buy something because a rumored upgrade 'might' be around the corner with no real factual basis only leads to one waiting forever. It's different than iPhones and iPads because we usually have a very reliable idea when they come out. However there's been nothing but very weak rumors of a new ATV for over a year so far.