While Diskspace is cheap, RAW files continue to grow as well. My take: Converting to .DNG is not a bad idea at all. Why, because you should have a backup of you images anyways, so why not have a .DNG as a backup that does conserve some space at the same time. I would like to think that .DNG will not go away. It is such a common sense, no-brainer with respect to uniformity across software editors. Over time, if there are competing "open source" file formats, then conversion software will also follow that can convert .DNG to a new format.
Why it hasn't gained widespread acceptance is attributed to the proprietary attitudes of camera manufacturer's and the software they hope to sell to work with and view their
"special" formats. I have used many Canon cameras and find that there are many Canon RAW file extensions such as .CR2, .CRW, and some software will not accept both formats, especially with respect to viewers.