Updating Youtube Video Keyword

Does it have huge impact updating old videos by giving them new keywords and adding more descriptions?

Or

Wipe them, edit a bit and reupload?

I found my old account with low view and i think it's valuable resource.

Yes you can private the older videos and re upload them with new keywords.

For views it's better

I updated titles, descriptions and tags of half my videos about 10 days ago. So far I am not seeing any issues, I am not ranking for the new keywords yet but I am still ranking for the old ones.

You shouldn't have any problems but I don't think that you will instantly rank in top for your new keywords though

as far as we tested, youtube index service (or the ranking algo) will treat new videos completely differently than old ones.
as you upload a new video it will be tagged with a label "NEW", and that that time youtube will decide about it's ranking positon
on the same time you will be able to "Play" with the tags and kw and see that it's affect your position as youtube will re-index them.

Old video on the other hand, are already "dead" in a way, they may move a little if they get boost in traffic, but it will be slower if at all
so the best choice is to reupload (after spin - you want youtube to think that this is a new fresh content)

It's easier to boost new videos with new title, description etc.