If strings become blackened, they must be replaced. Fingerboard and frets can be cleaned and polished with 0000 steel wool after removing the strings. The only place for a tamburitza when you are not playing it is in a closed case. Some of the most serious damage occurs because an instrument is left on a chair, in an open case. Always be aware of what is going on around you.
Serious damage can happen because a music stand hits part of an instrument.
Especially vulnerable is the soft spruce top. The edges can chip and break with more ease than the harder maple back. The varnish on your instrument does a great deal more than add beauty to the bare wood. It protects it and adds to the sound. If bare wood is exposed, either because of wear or damage, it is important to have an experienced repairperson add color and varnish to those areas.