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 😁

The Spirit Bomb is already OP as it is, but gathering energy from your teammates is a very interesting and simple idea. I like it.
I think I'll use the FX I'm currently programming to show the healing of teammates in the background, creating small light blue spheres that move from them to the Spirit Bomb. As for the bonus it gives, I'll decide on that when I work on it.