But do I need a visa to get into Taiwan with my ROC passport?
Actually what is the point of an overseas Chinese having a ROC passport?
I will give you my answers on the basis that this is the case for overseas Chinese from the Philippines though I strongly suspect it will apply to most overseas Chinese all over the world.
With your ROC passport (without Taiwan National ID), you are considered a ROC national but without a right to live in Taiwan, cannot work in Taiwan, and cannot vote in Taiwan. You are allowed to visit Taiwan though.
To visit Taiwan using your ROC passport, you need to apply a Visitor Visa with TECO in your home country with your ROC passport. This visa is free of charge and you will be allowed to enter Taiwan with that visa in your ROC passport to stay not more than 3 months.