Almost my entire guild has returned to Tyria. We've all gotten the majority of characters the masters on all Canthan missions so we've returned to Tyria to get the Protector title on the newly made Canthan characters. This entire past two weeks has been spent in Tyria, and while it's much easier then we remember it; we've been having some really good laughs and fun re-doing the missions.
Tyria will probably become, as you said, Ghost Wars with the release of more chapters. This really can't be helped though (too much anyway) unless new content is constantly added backwards. I've played many online games (MMOs) and this always happens. New expansions comes out and people move to the new stuff while it's new. Most don't want to play the "new" stuff when it's 3 months old... it's not "new" at that point so they don't care as much. /hint at Anet for opening Elite Missions /end hint