I think a simple 3 point fill setup of suns would do a nice job, about 0.25 strength. But, as Frank said, you really need GI to take things to the next level.
I really need a new computer to take advantage of the GI in TG again, I rarely do a full final render with GI anymore due to limitations of my machine, I just can't afford the time it takes on this old beast.
Most of my renders for about the last 6-7 months haven't used GI at all, I've even found ways around it when using clouds. Still, I'd like to be able to crank the GI up again.

Nice scene setting. AA about 8 would do it wonders.(9 is a strange number, Frank, that I wouldn't normally use for AA, although, it'd look better, of course.

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