Gold is pretty much maintanince free if you treat it well.  It is normally plated on over an underplate of silver or nickel.  The gold and nickel underplate are quite thin and will have a minimal effect on the propoerties of the horn.  If silver is the underplate, it is thicker and may have an effect (see silver below).  Gold is (or was) occasionlly plated over raw brass, a practice which frequently eventually results in a dull finish which I don't particularly like.  Plating over silver somtimes allows the silver to tarnish under the gold making it look as if the gold is tarnished.  It is easy to remove that with a liquid tarnish remover like Tarnex, but do not attempt to polish it off by rubbing or buffing or you'll take off the gold to get to the silver.

Lacquer will usually show wear within a few years and tends (IMHO) to look a bit scruffty after while; however, it is a beautiful finish on those instruments which use a mixture of alloys such as brass and nickel on a Bach Strad or a Kanstul copper bell.  It is fairly thik and has properties quite different from the bell material and may have subtle effect on sound.

Silver is, for many people, quite durable and can be polished to look good for years; however, many other people have a body chemistry which reacts strongly with it causing rapid damage to the silver and underlying brass (as well as the skin).  For these latter folk, gold a lacquer are better. Silver is frequently plated on quite thickly and may therefore have the effect of stiffening the bell and making the trumpet sound "brighter".

Regards,

John Lynch