This may or may not be relevant to you but for a long time I was auto-converting my CR2 files to DNG during Lightroom import (without embedding the original CR2 in the DNG since I was doing it for space savings as you are thinking of doing) and now I kind of regret it because the "Digital Lens Optimizer" that ships with recent versions of Canon's DPP is actually really good at pulling out image detail that Lightroom or ACR doesn't give me in the demosaicing process on photos taken with Canon lenses (since only those have 'DLO' profiles). And DPP doesn't support DNG loading.
Granted, Lightroom/ACR still do a very good job of rendering RAW files, so the difference isn't that great without pixel-peeping, but it might be something you want to think about when it comes to switching formats.
I've since gone back to importing the plain CR2s as my on-disk RAW format -- in practice CR2s are more universally useable than DNG files since not everything can read DNG whereas since you can always go from CR2->DNG, everything that can read DNG is covered by CR2s.