You are better off actually knocking down your SoS and placing lvl 4 guilds on those lands, and then just hit Haunting or Ambush and try to buy your Highlands out. If you want the stats however, then knock down anyway and build volaries on your highlands. If you choose the second route I advise that you save up and build your volaries straight to lvl 2, especially if you are placing it instead of a lvl 4 guild.