I thought USSJ wasnt neccessarily slower and stonger than SSJ. The way I see it, Trunks erred by making himself stronger, thinking that he could beat Cell with strength. He was stronger, yes, but he was too slow as a result to be able to figh him. Goku and Gohu, if I remember correctly, didnt power up their strength, but realized it would take more than strenth to take Cell and therefore worked to be faster when they powered up.
I heard SC:CT was excellent, but that was in a SC add... but back to the topic...
Perhaps when you go USSJ you get a menu, not unlike with the dragon balls, and can decide which areas to power up. Speed, to make your adv melee arrows more random (except against similarily powered up USSJ), or power, to increase the damage dealt by the hits you do land. A third catagory, for those who like their beams, that would give you a larger PL multiplier. Just a thought, but it would make the transformations feel more like a choice rather than just another power-up.
Of course, you would need to add something to deter people from just transing again to change their choice. Something that would fit DBZ, like a trans stamina meter. You can only trans so much (based on you PL) before having to rest. No more rapid-fire instant trans fun, but Id get over it. With this, you would have to pick your power-ups wisely as going USSJ, or any trans for that matter, is a major power drain to the average saiyan.
But my whole view of USSJ could be wrong... Im not exactly an anime buff.