I'm confused about your position. It sounds like you're complaining that the IT world did all that work to make sure that everything ran smoothly. Are you saying we shouldn't have, and should just have dealt with any problems as they cropped up? That makes no sense.
I'm saying we (me and my group) did a bunch of work testing, re-testing, placing contingencies, updating, backups, etc. for nothing.
Yes, we would have been money ahead to fix problems as they cropped up. And you'll probably say that had we not done all that testing we wouldn't have known--fair enough, but we still poured a ton of resources into it, even after we told the plant that the risk was of a "Y2K bug" was very low after our first round of investigation.
Except for IT/Plant Floor overlaps, our interface with IT was not extensive--they had their own team, so I cannot speak with authority of all the issues they encountered. But my perception was that there were would have been hickups on 1/1, but nothing would have crashed, no data would have been lost, no body would have been injured, etc.
YMMV.