Smarts and intelligence can be seen attributed to different aspects and behaviors, but we all generally agree and know when someone is smart and when they are not. If you have observed that you are frequently the smartest person in meetings and on projects (assuming a great degree of self-awareness here) the time may have come to consider finding a different room.
Continuous challenges and opportunities to learn and educate yourself is what will make you grow, improve and advance. Staying on the same level which you have already mastered will only stagnate and limit your potential and possibilities.