Not sure if this is a bug or intended but recast abilities do not benefit from the extra spirit power/range/duration on Arcane Surge. Abilities that I have tested include:
Sinclair’s Audience Participation (4)
Apollo’s Flawless Advance (3)
Mina’s Sanguine Retreat (2)
Mirage’s Dust Tornado (2)
It’s hard to tell but from what I measured Mina’s Sanguine Retreat only seemed about half a meter shorter, so it might be benefiting from the range but not the spirit power? (Gets 0.4 meters from the 20 spirit power.) If someone could try measuring it with debug or tell me how please go ahead.