Dual spec is in my opinion way to overhated. All it really does it make player have options to swap to their Pvp specc without having to waste a character slot on your account.

It allows raiders to be more efficient PVP'ers. As I remember it, sure I had some of the best gear on the server but I couldn't just go and stomp people who were committed to PVPing because my spec was gimped for that. I also had a harder time farming in the raid spec. As well as the gold sink.

Did I hate it back then? Sure as hell.

But if it were added to a "vanilla/classic" version it would completely change the balance of PvP and the economy. For better or worse? No clue, but it sure wouldn't be vanilla. And I figure PvP'ers wouldn't be a big fan of geting stomped by raiders.