In my opinion; an increase in turn speed, and increase in acceleration, moving the right gun arc more toward the front (without allowing a mercury to make trifecta but perhaps allowing a mortar) and reducing the hit box would be a good place to start.
This will allow the Spire to dodge rams, take less hits, and make it much easier to make captain Trifectas. Even with all of this the Spire likely would not rise to top tier but it may make it more competitive.