The Arcane Tower has been in a very strange spot for a while now. It saw a lot of activity last year, then died down sharply. I can't profess to know why RP is hard to generate and sustain there. But I do have some observations of my own, and from talking to others. Let's ignore the history of why the Guildhall dropped.
Forgive the bullet points, but it's 7am and I haven't finished coffee. I just want to put thoughts down.
Too many tiny quarters - leave no room at all for fixtures, might as well just buy a bank vault. Same size.
Replace the tiny quarters with bigger rooms similar to what is in the second floor dorms. If that means fewer rooms, no great loss. There's still tons of quarters.
The Tower is big enough to be a settlement, but there doesn't seem to be any great, quiet central point for gathering and RP that isn't a classroom. You can get out of the way, but with how the Tower is set up, if you do that it's very very hard to stumble across your peers.
Seriously, the Tower is bizarrely huge. Ground floor, Common Rooms, Hall of Memories, Warden's Hall, Exterior, Apex, Arena, Hall of Countenance, Hall of...Other Word (lack of coffee showing), Menagerie, The Love Shack, Observatory, Chef room off from the Menagerie, I think I'm missing a distinct area, but you get the point. It's huge.
The Tower should be a central focus for mages on the surface to gather, regardless of city of choice. What can be done to encourage that instead of splitting into 3 or 4 city-based much smaller groups of mages? Why would the mages of the surface congregate at the Tower instead of staying in their city?
Give the Tower some quest mechanic similar to Sencliff, but mage-focused. Something to have its inhabitants work towards and progress at something.
Other interesting/fun mage mechanics being added would help. Yeah, there's the Map. But uh...yeah.
Is there a reason the portal isn't a two-way portal?