NAS or...?

Technology dilemma of the day: how to increase network storage for 500+ incoming DVD images.  NAS?  Or just more disk on the existing server?  Or a new server?

External enclosures for up to 4 drives are pretty inexpensive.  I can attach one to my home Ubuntu server via an eSATA port.  But I think I will end up having to do software RAID for that.  Most of the enclosures I have seen do not get high marks from reviewers for their internal RAID abilities.  If they even have any.  Of course I can just use it as JBOD, but that really makes me nervous.  It's not that the data will be irreplaceable: once ripped, the DVDs will be stored, not sold or donated.  I will honor the spirit of the copyright law.  It's just that redoing it will be so damn much work.

The alternatives are things like the QNAP TS-451, which will cost enough that it makes me wonder. should I just build another server?  But two servers for a residence of  two humans and two cats seems excessive.

Help! Say random things in the comments to nudge me in a direction that will get me to a solution.