Not at all. Good things last. All the 100 year old crap has long since decayed. By definition, if its been there 100 years and still works, its probably pretty good.
Points about making sure the cable sheath is earthed, and making sure its on a modern RCD system, are good. I've seen brand new PVC cable eaten to a short by rodents.
Obviopusly if you are into a complete rewire, take out old stuff. But its stupid to replace things that are working OK just because they are made in a way you don't reognise. ESPECIALLY if they can be backed up by a modern safety system.