The interpretation of the Page of Cups in this situation suggests that the question is yes. The Page of Cups represents enthusiasm and creative energy, so it's possible you need a new musical instrument to better express yourself. The card also depicts a child who is curious and open to new adventures, so it might be worth buying a new musical instrument as a way to expand your creativity.
Interpretation of the Eight of Wands in this situation suggests the question is no. The Eight of Wands represents resistance and fear of change, so there is no need to buy a new instrument. The card also depicts people who are stuck in a situation and can't move forward, so you may feel uncomfortable with change or fear expanding your capabilities with a new tool.
From the interpretation of the two cards, it seems that the answer to the question is "Yes". The Page of Cups encourages taking a risk and exploring your abilities with a new musical instrument, while the Eight of Wands suggests not changing things too much, but rather focusing on building your proficiency with your current instrument. Therefore, it is recommended to follow the message of the Page of Cups and buy a new musical instrument to further develop your creative abilities.