So I have an idea for an online service that got me excited. However, I feel the idea is kind of dumb when I think about because it's so basic/simple (but new). Should I spend more time enhancing the idea or go ahead and execute?
Impossible to say. Doesn't really matter if the idea is elaborate or simple, new or old.
You should be asking these questions:
(1) Should people use this?
(2) Will they if I reach them?
(3) What will it take for me to reach them?
(4) Will they value my service enough to repay my efforts?