Is the intention to please one's parents and bring joy to them considered a good intention for studying and achieving success in worldly knowledge, especially if their primary motivations are social appearance, or are only the intentions of benefiting people and serving Islam acceptable?

Your diligence in studying with the intention of pleasing your parents and bringing joy to them is a good deed for which you will be rewarded. It is part of the dutifulness to parents commanded by Islamic law, and it does not contradict the intention of serving people and benefiting Muslims. You can hold all these intentions, and you will receive a great reward for them.