I don't really understand what a "directional dome light" is because they are clashing concepts in my mind. And as far as area lights go, the main things I keep in mind are:

*Size affects intensity, the bigger the brighter.
*Size affects shadow softness, the bigger the softer.

Once you've adjusted the postion, color, size, falloff and intensity accordingly, its pretty much all fine tuning the samples to ditch the noise

In this case, you could try plopping one down for the sun and another faint light blue one for the starlight for starters.