I know I'm late to reply, but, as long as you don't care that you'll only be able to play 720p, and no more software updates, get it...
This is pretty much true, the confusion is that, while the 3 has an "A5" processor, it is only single core, thus, almost the same as an A4 (same speed mark test scores). [The main difference between A4 & A5 is single core vs dual core processor.] The ATV2 has 256MB RAM, 8GB storage, ATV3 512MB RAM, 8GB storage, so this would be main reason for 720p vs 1080p (and more features, see next para.) The 2012 ATV3 was made with a dual-core A5 processor that had one core "turned off" (same A5 could be put in various apple products). The 2013 ATV3 had a smaller single core A5 processor and other component tweaks that made it cheaper to produce and lower power consumption. (source: http://9to5mac.com/2013/03/15/impli...le-tv-lower-cost-new-a5-chip-ramping-numbers/
That being said, the following features are only available on a new ATV3, (besides 1080p), you can continue to get software updates, initial set up via beacons (just put compatible iOS device near it (wifi & bluetooth on), it will set itself up after you enter your iTunes password on iOS device.), family sharing, and people w/iOS devices can AirPlay to it without being on your wifi (also, Beats music channel if you care) http://support.apple.com/en-us/HT202157
Apple often has ATV3 in refurb for $75 w/same warranty as new http://store.apple.com/us/browse/home/specialdeals/appletv
So, while $50 is decent for adding AirPlay and streaming 720p content, $75-100 will get you 1080p and a little more.
(On a similar note, the A5 processor, while it is in iPad 2 & iPad Mini (1st gen. non-retina), everything else about the iPad Mini is different, so the Mini can do AirDrop, full handoff & continuity, while the iPad 2, older board design and only has BT2.0, can't do AirDrop and some other features.) The processor is not the device. Ahem. You can find and Intel i7 processor in a PC or a Mac.