I think it would be nice if goku's spirit bomb was able to gather the energy stored from other teammates during the fight, like it happens in dbz against buu or dbGT with omega shenron, making for a bigger sphere and higher damage output. Since it might become too op a way to make it more viable would be being able to use only one extra energy bar per teammate and require 2 special bars instead of one.
That's about it 😁