To me the gameplay feels almost like Mirror's Edge in 2D. I think the lack of responsiveness people are experiencing can be attributed to the amount of air control and slower directional changes. If you're used to knytt stories, air control and directional change are done on a hairpin, so to speak, so I can see how the change can be unsettling. I for one love Saira's gameplay just how it is, please don't change a thing.
As for the power-ups, I think the original Saira episode is fine without them. For third party episodes however, I suppose anything is possible as long as it suits the gameplay.
- Inph