One addition that I thought would be an easy win, was some patches of dirt on the flagstone floor, but it turned out to be more of a pain than a win.
Here's the first attempt:

Looks too much like piles of sawdust, and there's a weird glitch where the grouting is being hidden by the supposedly transparent part of the pile.
Take two, with the transmission of the dirt objects dialled up, to try to make the edges more transparent:

Now it just looks like the aftermath of Adric drinking too much Venusian ale.
Third attempt, after making the dirt image more transparent before importing it into Blender.

Looks a lot more like leaf dust on the floor, but the problem of the grouting being hidden by what is supposed to be transparent pixels is still there. If you look closely you can see the straight edges of the back dirt patch, revealing its actual rectangular shape.