This might just be me, but if you have a perfectly good two year old phone. Why did you buy a new one?
I recently bought another battery for my Galaxy S2 because the old one died. I have no plans for replacing that phone until I absolutely have to. Preferably not until there is a Samsung Galaxy S6 or so.
Hehe, I still use my Galaxy S (one), which appears to be indestructible. Several falls on concrete did not kill the phone. Also, the battery is cheap to replace, so I always have an old backup battery with me.
But most important, it's rooted and runs Android 4.2. Yeah, it's a little slow, but upgrading wouldn't change all too much. 400 USD for a little more speed on the same functionality? Naah ... All my previous phones like ridiculously old by now, but even the most recent devices only differ in detail from my good old Samsung ;)
Yeah that is pretty much what is keeping me from upgrading.
My S2 is still fast enough to run anything I've tried.
What would I get by buying a S4? A bigger screen, 4G access and NFC? Other then that I am not really aware of any benefits. I run CM nightly anyway so in terms of software it's as good as the new phones, and I only ended up running custom firmware because Samsung stopped doing updates.
Really it's not in "perfectly good" condition. Broken screen, broken usb connector, bad battery life, water damage that causes the cell radio to intermittently not work.
I recently bought another battery for my Galaxy S2 because the old one died. I have no plans for replacing that phone until I absolutely have to. Preferably not until there is a Samsung Galaxy S6 or so.