The cost of getting an interface for recording the output of VHS, and the messing around you have to do to get it to work properly (macrovision and all that) far exceeds the cost of buying the DVDs from your local charity shop that you can't find a torrent of (shouldnt be many), and the quality will be massively better from the DVDs than the crappy quality you will get from the VHS tapes (particularly if they are worn).

You digitise VHS when you have no other choice - there is only one copy of it. For the stuff mentioned as examples - the vast majority of which should be easily torrented - there is no reason to go digitising the vhs.