Huh... I must have been tired. I looked through a number of them on that site, and I meant to find one comparable. Given the current price of ram, 8GB does help. I don't place much value in a hard drive that is more than 2 years old. They do eventually wear down and begin to develop bad sectors, even if they don't fail to mount. I would have rated that point as little more than a push unless it was fairly new.
There is always a certain amount of risk in buying a used machine, particularly when there is no available recourse in the case of latent problems which are not immediately obvious when previewing the machine. Most used mac retailers tend to offer a 90 day warranty to compensate for that, even if it's a minimal length of time. Batteries often need to be replaced regardless of how much charge they still hold. I've had to do it due to swelling. Sometimes toward the end they do take a dive. It's something I would expect around 3-4 years, so it's definitely a consideration. They are more likely than not to require a new battery if they keep the notebook for the same amount of time. Anyway I don't think it's as likely to sell at $800, at least not quickly. It would be more likely on ebay, but then you have transaction fees and the risks inherent to ebay.
Well I think I found the same model as the OPs and according to that site, they;re selling their Mid-2010 13 MBP 2.66GHz, 4GB RAM, 320GB HDD for $749. So if you factor in the cost of another 4GB RAM and the larger HDD, then I think (at least according to that site) that $800 is still more than reasonable.
However, that same site is selling a 13 retina MBP 2.4GHz i5 with 4GB RAM and a 128 GB SSD for $1,199. So I have no idea what their pricing scheme is really and how they termini a value for each specific part.
Even though I like screen clarity and crisp detail, I think the current lineup of cMBP have awesome displays and retina is one of those things thats not really a necessity. Plus, with the purchase of a retina MBP, you lose the built-in expandability and the user-upgradeability that the cMBP offers.
with the FW 800 port, you can connect to TB/FW800/FW400 devices and the usb 2.0 ports allow for connection to any usb device as well. with the retina MBP, you would need a separate adapter for each peripheral.
Of course theres always a certain amount of risk involved when buying a used machine, but not trusting a HDD after 2 years really limits options for computer purchases. Sure some HDDs are cheap enough now where they might not be that big of a deal to replace, but there are some amazing deals out there. For example, I was able to get a PowerMac G5 Quad with a 1TB HDD, 8 GB RAM, AND a 23 ACD for the incredibly low price of $200. Sure, I ended up buying more RAM and bumping it up to 16GB, but that machine was great for as long as I was able to hold onto it.
I also recently (5 months now?) got and sold a PowerMac G4 Quicksilver from 2002(733MHz with 1.5GB RAM and a 40 GB HDD) to a friend and he has made that machine AWESOME. he upgraded the CPU to a Dual Processor, SATA cards, 4 HDDs, 3 displays
etc. And he got it from me for $50 + 2 iBooks.
Anyway, I understand why you would consider the value of the OPs machine to be lower, but my experience with much older Mac machines has given me a very different perspective on actual value based on usage and potential usage and I go higher on the value because of that.