On reflection, I think it will not hurt to up the healing sphere to 15 health given per sec instead of 10, and reduce the cost from 9 to 7.

At the moment the return back from the blast far exceeds the sphere. With this change, running a sphere for 7 seconds will give everyone in the sphere 105 health. A blast for the same cost will typically heal the same people between 100 and 300. So we are not giving more points to medics, just increasing their options. But it may encourage other players to throw their adrenaline at the medic to keep the sphere running.

Similarly, I think the damage sphere could come down from 12 per sec to 10 per sec. A damage sphere will not stop players getting killed, but can get them out of a tight situation.