Sometimes, a floor with shallow scratches or a dull surface only needs a top coat of finish. Other times, refinishing isn't enough and whole boards need to be replaced. If scratches or dings are in the wood, refinishing is the next step. However, a wood floor can only be refinished so many times because each sanding takes off more wood. Check at floor edges or around a heat register to see how much wood remains.
Maple floors are difficult to sand and stain well.
Consider hiring a professional to refinish them. Since variations in temperature and humidity cause the wood to expand and contract, small gaps and cracks do serve a purpose. Winter months tend to be drier making cracks and gaps more visible. In summer, humidity rises, causing some cracks to virtually disappear. Large cracks in the summer however, only lead to bigger cracks in the winter.