Gold in Virgil's poem symbolizes what is special, hidden, and
rare. This can be seen in the golden bough stashed away in the
deepest, darkest corner of the forest, which only the designated
person (Aeneas) can take to guide him in the underworld.
(Though, of course, there's that whole ambiguity over whether it
comes off the bough of its own accord, or whether he has to
snatch it off.) Through the motif of the "Golden Age" which
faintly persists in the civilization of the Arcadians on the
future site of Rome, it increases the sense of the Trojans'
homeland as secluded and important. You can see how significant
it is when Virgil tells us that Caesar Augustus is going to
bring about a new golden age – he's going to make the rarest and
most special thing available to everyone.