Loving your improvements so far! So much that I felt motivated to do a lil' edit myself (I hope that's ok).
I've changed the
middle floor as I saw you were having a rough time with:
1. board ends. At this "zoom level" the cracks shouldn't look so deep. To create a milder effect without completely erasing the gaps, I've used colors with closer brightness and saturation values.
2. nails. Got rid of them! "Zoom level" was again the main issue. They were looking more like lost pixels than nails. If you want to keep than anyway, I think they'd probably look better if you'd use the same technique described above.
3. focal lighting. I like it! Draws the attention to the middle of each room and the darkest wall shadows help making the sliced walls pop up. In this particular bit, I didn't do much, except for dithering the areas between colors. I've also took one of the wall hues and used it on the floor as an extra gradient step. One thing I've noticed while doing this is that if you increase too much the contrast between the darkest shade and the brightest spot in the middle, the floor starts to look like a sphere.

OT PS: Ground humidity makes boards rot. That's why castles always used stones or stomped (is that the word?) dirt on ground level floors.
OT PS2: Do you plan to add some nice wooden stairs? It would look soooo cool!