defcon

You don't need to build your own pc, there are many sellers on ebay selling refurb pc's/servers, it all depends on your needs, budget etc. e.g. you can get a Lenovo ThinkServer/HP workstation for cheaper than you can build your own and it will have better build quality as well. If you think you want a lot of drive bays for future use, there are many other server types.
 
e.g. http://www.ebay.com/itm/HP-DL380E-G8-2x-E5-2420-12-CORE-16GB-NO-HDD-H220-LSI-9205-8i-/172542645101?hash=item282c57d36d
 
For $330 you are getting a modern cpu, 16GB RAM, 12 hotswap 3.5" drives, and industrial build quality, you can't really build anything close to this. The downsides are going to noise, but depending on the server there are ways to quiet these down. 
 
Just another option to consider.

Even is Storage Spaces was a one click setup, I still wouldn't use it. It has the same dangers as any other solution that stripes data and doesn't keep individual disks readable in a normal pc. RAID with striping, ZFS etc all have the same dangers.
 
The big advantage of DrivePool is your data is always in good old NTFS. No rebuilds, no dependency on hw, and no need to repair an entire array if a disk goes bad. You can take out a disk any time.
 
SS/ZFS/RAID were all designed for enterprises, and are not meant for home use. Besides the data dangers, they have higher costs - in disks (needing to match disks, replace multiples), hw and running costs.

Ideally I'd have everything backed up offsite or offline. But like I said, that needs a 2nd server at least, or managing a bunch of externals and keeping track of which one is filled up when its time to take a backup. Its simply not feasible after a certain size.
 
Most of the time deletion is deliberate - e.g. I delete a movie after I'm done watching. I am willing to live with the dangers of accidental deletion. Actually I think if I use snapraid and have it do a nightly sync/scrub, then it can reconstruct accidentally deleted files because parity is not realtime.
 
But to me the main advantage of duplication is its actually 2 copies of your data which is the most secure form of protection as you don't need any reconstruction. And its effectively a backup since I can resue the disks on other pc's. If it doesn't serve as a kind of backup, then am I gaining much vs a parity solution? After all we are using 2x the disk space.