Can boost and spindash exist in the same game together? They kind of clash, being both speed up moves. But if you underpowered the spindash, and made the boost more limited, it could work. Say the spindash was the same button as the boost, but you could only use the boost when your gauge was full (which would take 40-45 seconds to fully recharge). When your gauge was not full, you could press and hold the button for a spindash ala SA2. This could also be used to gain speed when you don't want to take the time to fully accelerate while running. The spindash could never go as fast as the boost though, so it's not overpowered.
So anyway, what do you think?