Yeah, maybe Sparda is balding... after millenia, it is understandable...
As for Vergil's white hair... dunno where it came from. Maybe it's a demon thing: after all, Dante starts showing white hair after unlocking his DT... But, no it doesn't make sense, Vergil had white hair as a child, and I doubt he unlocked his DT at the age of six...:/
Maybe it just comes from Sparda, who had white hair, but started using hair dye.
Now that i think about it, it would have been terrible if Vergil had red hair like Eva. >_< (Nothing against redheads, but Vergil with red hair... ewww!>_< )