Oh! I see what you mean, yeah, the lighting on the water droplets caused some weird effect from that angle. That's going to start bothering me now hahah.I am also learning Daz and it's been a blast so far. Your photos look great, but the first one up close looks best. The other two look a little off because of the water effect on the girl. It might be lighting causing it, and i have no idea how you would fix it.
The billboards don't look bad, i honestly didn't know until you pointed it out. I might have been looking at your main subject... I do think you could fix the shadow issue with a small spot light on low pointed in the right direction or at lest not have a shadow in the buildings shadow at all. I mean who do they think they are, Shikamaru???
About the billboards, thanks! Yeah, I tried my best to just have them at non-important/filler locations, for example, the 2 random pedestrians closest to the main characters are also 3d models, because they were too close for me to feel comfortable sticking with billboards. I did a similar thing with the cars, the closest one is high resolution, while the ones far away are very low resolution.
The idea of putting some lighting to force them to cast the shadows I want them to cast is pretty interesting! I'll try it out, thanks!