You're right - those files have not been touched since the fork. Three of them were last modified in 2000, one in 2003. And yes, we could send those guys letters, but since what they contributed to was Sodipodi, I don't think we should.
Why not? Just explain the difference between the two programs and let them decide for themselves.
And by the way, why limit ourselves to 0 or 1% ones? I think we could send such a reminder to every translator in our database. (Well, except for those who are already very active :) Some of them may simply not be aware of Inkscape existence, and those who are may not know that we're nearing a release so it's high time for translation contributions.
One thing we could do is to check the current Sodipodi translations, but I don't know where to find them. Anyone?