Do not, repeat do not, systematically polish a guitar with a wax polish, whether furniture polish or any other kind. Eventually a layer of wax builds up. This materially reduces resonance, at both ends of the scale, and results in a boxed in sound. I am at present polishing with care a 40 year old guitar I inherited, each time I change the strings, in the hope of eventually getting back the original brightness. An hour with white spirit a fortnight back made a great improvement, but if you use white spirit on old guitars beware of lacquer cracks and crazing, and do not use a modern guitar polish for at least a week afterwards to allow all the white spirit to evaporate from the cracks. My belief is that if any white spirit gets into the wood it will do no harm and evaporate from the unfinished side (inside) in due course, but I'm not going to keep on using even a gentle lolvent like white spirit any longer than I have to.