Not that I care either way, but I thought I'd offer a dissenting opinion here and say that the used 2011 deal doesn't really sound like a terrible deal. It's got discrete graphics, a RAM upgrade, and a 256GB SSD. The refurb 2012 is $680. So based on the prices others here have quoted, you're looking at close to $1000 by the time you add the $45 8GB RAM upgrade, $200 256GB SSD, and then the kit to install that SSD (or did that $200 price include that?).
I think you need to decide which features you really want/need. A lot of people here are saying the SSD upgrade is pretty easy, and maybe it is, but if that's important to you, you need to factor in your comfort level in doing that upgrade yourself. Lastly, is the seller's $775 price on that used one firm or can you talk him down even more?
Personally, I just got a base model (i5) 2012 open-box Mini from Best Buy for HTPC/media server purposes. The i7 would have been nice, but I wanted to squeak by as cheap as possible (got mine for $460). I like the idea of having the latest gen model and USB3. I won't be playing games on it, so the HD4000 seemed good enough (and I actually kind of like the idea of having less "stuff" crammed in that tiny box as I would think it might run a bit cooler than having a discrete graphics card). The i7 vs i5 for me was about whether or not the i5 would be good enough for Plex to do some on-the-fly transcoding of HD video content, as opposed to wanting/needing the extra CPU power for productivity purposes (I'm a laptop guy for my daily work). It sounds like you're going to use this for productivity purposes, so going with the i7 makes sense.
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Just reread some posts here and saw you mention that it's missing a power cord, which sounds a bit odd. Know that the power cord is pretty standard. If you have a newer Apple TV (and maybe even an older one?), that cord will fit. If you decide you want to buy that used one, make sure you boot it up and confirm that all of the features they claim it has are definitely there.