[X] Stealth
[X] Defense
[X] Perception
We still lack a real Stealth Art, something to base our role as a spymistress around, something to capitalize upon our mists (because combat stealth is awesome).
Considering SCS, FVM, FSS have probable upgrades through the Moon Map and Ice!mom we are okay for the core of our Arts. So i see no reason to research things like "music" or "moon".
What we need to get is a replacement for TRF and AM.
Other than that, i could see as useful a research into Domains (an Art to boost our flying weapon would be huge), or Social "combat".