I inherited a couple Netgear ReadyNAS boxes 3 years ago and certainly do not regret purchasing the network attached storage. Coz. price fits within budget, lot of functionalities, centralized backups, data redundancy (go with RAID or not its up to customer), ease to use and performance is great.
By RAID5 approach we could get only 1.4T of 500GBx4. I would rather prefer 1.5Tx4 and align storage schedule in 4 drives separately. So Sun to Wed storage schedule from disk 1 to 4. In the event of a disk failure we can rely on other 3 disks.
OR RAID0 configuration - 1.5Tx4 with 2 volumes of 3T=3Tx2. This way storage schedule can be pointed to two volumes relying on 3Tera redundancy. If RAID5 with 1Tx4 we could get only 2Tera approx and a redundancy of 4 disk which is actually not required in terms of a network storage.
Here I opted RAID0 as we have a separate storage share where backups are stored. So even if 1 drive fails i can still rely on the other storage share.
I have used ReadyNAS NV+ second box with RAID5 config where all critical storage happens and from there the data is collected to tape
Netgear ReadyNAS FAQ http://www.readynas.com/kb/home