If you do it on your own there's not much you can do apart from transferring the video to your PC/Mac and maybe fiddle around a little with editing software to make the image brighter. But when it's out of focus it is out of focus.
If you have too much spare money you can give the tapes to professional studios and let them transfer the tape. They have some serious equipment at hand, but they can't do anything about the focus as well.
Either way you should make digital copies of your tapes to preserve them. Just reminded me of buying a VCR, as my old one is broken since a couple of years.
Or I buy the matches again from the producers - it's mostly DT so it's all available and ripped from the master tape for maximum possible quality
