I am under the impression that both "wegen" and "aufgrund" mean "because of." Is there any difference in their meaning or usage?
Both wegen+Genitiv and aufgrund+Genitiv are prepositions with that very same meaning because of. The latter is made from the words auf Grund. There is also an adverb aufgrund, which takes the preposition von+Dativ.
It's common to use wegen as an answer to questions leaded by weswegen and weshalb. It's an everyday word.
Aufgrund in contrary sounds a bit stilted. Don't use it in speech, it sounds as if you were giving an official statement.