I think the main issue is tape degradation over time. The miniDVs aren't classed as archival media, so the lubricants, tape backing, etc. aren't as robust over time as DVCam. Also, we haven't done so, but I'm told you're supposed to rewind and forward wind all of your stored miniDV tapes once a year, presumably to prevent sticking and so forth. (That would probably be a couple day job for us.)