There are some studies here that look into the long-term storage of information on DVDs. DVDs do end up suffering from degradation eventually - according some of these articles, you'd want to go gold-plated.
Personally, I would buy a few harddrives and use those for backup. You could even get a NAS that supports either RAID or JBOD (Just a bunch of disks) configurations and back up your data that way.
Edit: You might want to keep an eye on this question: What are my options for a multi-Terabyte home NAS?What are my options for a multi-Terabyte home NAS?, as the devices they're discussing are what you could use.