Oh man I hate to bring everyone down but apparently it's not that simple. It turns out that the reason Chi affects Superman is because he draws energy from the sun, so energy from the earth disagrees with him. In Dragon Ball, Chi doesn't come from the earth, but from every living being.
The spirit bomb can draw energy from the earth or the sun, so the biggest factor in deciding who will win is which one he chooses to use as a source. Unfortunately, he'd probably choose to take it from the sun, because he'd have no foreknowledge of it being Superman's power source and as a result would assume that it would be more effective.