One problem with Superman, in general, not only the live-action stuff, is his strength of plot. A bit consistency would be nice. Does he get exhausted? What's his maximum flying speed? His maximum strength? Why does he have trouble catching up with a missile, but then he can go in lightspeed around the Earth? One moment he looks pretty exterted lifting a car, the other moment he lifts and entire continent/island.
He does need some strict limitations, if only to have more in the way of challenges for Superman.
Superman shouldn't be able to reach speeds close to, exactly or beyond the speed of light whilst on Earth. I never liked the concept introduced in Smallville where Clark/Superman was fast enough to save several people in different locations all around the world and return within a couple of seconds. Not only does this cheapen the DC universe (if Superman is so fast, what is the point in there being other superheroes?) but it defeats the object of what the character is all about - namely that Superman isn't there to assist with any and every little thing that goes wrong, he's the guy who answers the big threats and stops the evil super powered characters that threaten the Earth whilst serving as a symbol of justice and inspiration.
With that in mind, a limiter such as the Sun-Earth EM field should be written in, in order to prevent Superman from moving at the speed of light (or beyond) whilst he is in the vicinity of Earth (and definitely whilst he is within the atmosphere.)