Resources are many and you don't have to conflicts between them. If NPTEL videos provided you that sufficient knowledge that you're able to solve GATE questions easily then don't read books.
Book actually helps you to have more detailed and rigid knowledge , but if your goal is exam specific , don't read them if you don't wish or don't have time.
but that is for sure book reading will make your concepts more sharper and if will boost your thinking ability.
Decide wisely.
