After years of agonizing over instrument goo ... I've come to the conclusion that the best goo is no goo at all.
Unless your instrument is raw wood, maybe oiled, the wood is already protected - by the finish. Nitrocellulose, polyurethane, French polish ... all seal the grain and keep it safe from the nasty environment. Slathering oil on top of the finish just gives you - an oily finish. It does nothing to further enhance or protect the wood. If you're lucky it will do no harm. But if you have any finish flaws - scratches, binding gaps, etc. - oil will just seep into the wood itself and may do more harm than good.
If the finish is in good shape, for routine care a damp microfiber cloth after playing removes fingerprints and normal playing gunk, and a soft microfiber chamois buffs to a shine. For non-water soluble gunk, a dab of e.g. lemon oil usually works. For maximum gleam, an occasional coat of pure carnauba wax does protect the finish, but may eventually create wax build-up. So I usually just let the finish speak for itself.
As Ahnko Honu says, unfinished wood like fingerboards and bridges do need some care. I use lemon oil, and only rarely, when the wood starts looking dry.
BTW, most luthiers will tell you that they HATE silicone. It settles everywhere on the finish and wood and in any flaws, and basically never goes away. And it makes future finish repairs and wood repairs more difficult, because it has to be removed first. Unfortunately, a lot of uke/guitar "polishes" and goo (not to mention household wood care products) contain silicone, often without telling you. Even some well-known brand names. So it pays to be careful, and know what you're slathering.
Just my 2 cents, of course.
