Old server parts for home server/nas build?

I was going through the internet, as I do, and I realized that the prices of old server hardware is crazy low. So I looked into what it would take to build a very high performance little server. Below are the parts that I found. I would like to hear what you guys think about the pros and cons to this approach. The obvious alternative is to go low power and small with a mini itx, atom build, or something like that. The two draw backs with that are performance (in case I ever need some serious servers, for WHATEVER reason, we are all enthusiasts here, right?) and cost (DDR3 ECC is expensive compared to DDR2 ECC).

Ram: 16x2gb ECC DDR2 (excessive and will leave some extra sticks, but it wouldn't be hard to find a use for them, also this seems to give the best value, though there are other options)

Mobo: Dual LGA771 (cheap, and seems like it would fit the bill)
http://www.ebay.com/itm/SuperMicro-X7DVL-3-Server-Motherboard-Dual-LGA771-Socket-DDR2-/400877843462?pt=LH_DefaultDomain_0&hash=item5d562e7406

CPUs: Dual E5450

Enclosure: Rosewill 15x 3.5" bays
http://www.newegg.com/Product/Product.aspx?Item=N82E16811147164

All of that said, I am none too familiar with older hardware, especially older server hardware, so there might be some compatibility issues with the parts I threw together here, however, my point remains. Could using old server hardware like this be worthwhile? Would the increase in power consumption and wasted performance make it a stupid idea? Would the life expectancy of a build like this be significantly lower than a build with newer parts (to a degree that it would be something to worry about)? Is this just overkill? And lastly, would anyone here do this/have already done this?