I'm not an expert, but regarding the fingerboard, I imagine that regular practice would do quite a bit to restore the colour and gloss of the wood - "natural oils", you know!
I sometimes varnish things (not violins), so drawing on that experience, I know that you can't just wade in with varnish - it's hard to tell whether you have spirit-based varnish or oil-based varnish, and while you might be able to put an oil-based varnish over a spirit-based varnish, you certainly can't get away with doing the opposite. (And you might find that along with the glue, things like modern synthetic resin varnishes have been used to "touch up" parts). So I'd leave well enough alone where the varnish is concerned.
I do use Hill's violin polish (just a drop or two on a cloth) occasionally, but you'll be surprised how much dust and grime come off just with regular practice - must be all the vibration, shaking things loose I think!
Don't use a damp cloth etc, as spirit varnish is susceptible to water damage, and the glue that holds the violin together is water-soluble (unless it's a really basic factory model built to take punishment).
Enjoy it, anyway, history and all.