To dream of being at the opera represents situations where you and others are expected to perfectly adhere to higher standards of maturity or more respectable codes of conduct. Having to blend in with rich people, snobs, weddings, good schools, or upscale events.
A concerted effort to behave perfectly intelligent, responsible, or sophisticated around other people. A situation that motivates you to behave or be more mature than usual. "Putting your best face on" for a special occasion. A area of your life where you feel the need to act perfect. Feeling good acting perfectly respectable or adult.
Negatively, dreaming about an opera may reflect peer pressure you feel in social situations that are dominated by rich people. It may also reflect your dislike of rich people or having to conform during special occasions like weddings.
Example: A young girl dreamed of having a knife fight at the opera. In waking life she dressed like a Goth and attended a school with a lot of students she described at "rich preppies." The opera reflected her school having lots of rich people with high standards for mature behavior that she was expected to conform to.
Example 2: A woman dreamed of her fiancee not wearing pants while attending an opera. In waking life she was about to get married and was having wedding rehearsals which she felt her fiancee was not giving a lot of effort towards.