One reason to remove the buttplate and at least check the condition of the stock, regardless of what you determine to do with the buttplate: Guns with horn buttplates can have worms that have made their way into the stock. A friend of mine had one of those. We referred to it as "wormwood". Was fine once the infestation was cleaned out.

I too agree that at least a strip and clean only makes sense on a gun over 100 years old about which you know nothing other than what you can see from the outside.