The general principle is that a repair maintains the property in as-is condition or restores it to as-was condition, while an improvement (a betterment) makes the property more valuable or extends the useful life of the building or its sub-systems. The improvement must be a permanent part of the structure (attached to or part of the house).
Paint and wallpaper is a repair, not an improvement. I would say the same about refinishing the floors (as opposed to installing a new floor which is an improvement).
Buying new appliances isn't either a repair or improvement unless they are built-ins.
Remodeling is generally an improvement, and if you do things like painting as part of the remodeling, you count them as part of the improvement cost, you don't have to count them separately as a repair. However, the dehumidifier is not an improvement unless it is permanently attached to or built in to the home.
