man, what are your electric bills?
The $300 you'd spend on a NAS/mini-pc would run my i7 desktop for 2.28 years, and that's assuming you don't plug in the nas/mini. Add in electrical costs and you're closer to 2.5 years before the break even mark.
Even my brother's 4ghz i7 with 6gb of ram and 5870 costs only ~$0.14/day to let idle