if you are concerned about your data you have to make a regular backup to another disk, but this doesn't mean that is has to be an internal drive. For example you can also backup to an external drive connected via USB, or a second NAS. As the MB Live is really cheap, this could be an interesting alternative.
Raid arrays may help you to avoid long downtimes, but as a home user this shouldn't be a problem and they offer no protection against virus infection, filesystem errors or accidental deletion. Besides there is another thing that you should keep in mind. At work we used to put cheap desktop drives into servers to save money. We were aware that those units weren't made to run 24/7 so that we decided to create raid 1 arrays. Of course all drives survived the 2 years warranty period, but then the disks slowly began to die according to a certain pattern: When the first drive in a raid array failed, it didn't took long until the second one went down too. In a NAS the situation is similar. You have 2 or more disks of the same type which all have the same usage pattern. So if one drive fails, it's probable that the other one will fail soon too.
Personally I use my MB Live for data exchange between multiple clients and for timemachine backups. So there is nothing on it, that can't be easily recreated.