Minor Repair~Scratches~Dings~Worn Finish
Most wood that has a finish applied has it there for more than one reason. Foremost should probably be to protect the wood and second would be aesthetic appeal (I love spell check). Depends on your priority I guess. Wood that sees a lot of handling and is highly mobile, like hoe handles or musical instruments will over time get dinged, scratched or just plain have the finish worn off. Some of us will accept some of this as 'battle scars'. Some will need attention.
In my limited experience with dulcimers, I don't see many that are coated with a finish inside, so I'm not going into protection from moisture at this time in this discussion. We'll first examine the exterior of the instrument.
There is a definite difference in the wounds we inflict on our dulcimers. A scratch will either be superficial, maybe not even through the finish, but it can go deep and actually remove some wood. One problem with tending to this is ... coloration. Wood ages and changes color. Wood is very often stained to change or enhance color before a finish is applied. A scratch that goes through the finish will almost always show a different color wood. Matching is VERY difficult.
A dent or ding is when something comes in contact with the wood surface, pressure or force is applied and wood is compressed as a result. A dent can often be steamed out to a level which actually exceeds the level of the surface around it, sanded smooth and sealed with a finish. I would caution against steaming near glue joints. Hide glue may take offense and decide to give you a REAL problem.
Wear comes from handling. When the finish is actually worn away it exposes an area that needs protection badly because it is susceptible to oils and perspiration from our hands. That's bad as it will discolor the bare wood and over time actually cause it to soften.
Now ... on our dulcimers add the extra headache of the many different woods and materials used often on the same instrument. I'm seeing some very exotic woods. Some of which I recognize as toxic when handled or sanding dust is breathed. Some of the woods contain natural oils which can't be finished or refinished until some sort of sealer is applied to the wood.
This is going way long, so I'll look to others to join in, offer views, opinions and 'fixes'. I just felt that this is could be viewed as a separate area from normal day to day cleaning and deserved a discussion by itself even though related.