The definition you gave is right. It's basically a figurative usage of the verb "revêtir," but honestly it's rarely used with words other than "importance." It's also better to say "revêt une grande importance" than a basic and meagre "a une grand importance." A decent alternative would be "est d'une grande importance," or even "est d'une importance capitale." The expression you mentioned is the one you will come across the most (especially in news articles), and it's one of those expressions that you simply remember and use in the right context.