That looks great Evert-Jan!
Indeed, dust in nooks and crannies doesn't go together with shadows. So, you have to choose carefully where to let the dust gather and where to keep the shadows.
One thing that can guide you is the amount of contrast you can get. Dust creates a lot of contrast on dark surfaces, while shadows create more contrast on light colours. So, applying dust works better on dark items than on light items. And light items often work better with shadows, because dust would be nearly invisible on them.
You have done this already: the bollards are very dark, causing shadows not to give much effect here. But the dust does!
On the photographs, I don't find the effect on the bollards exaggerated at all. Looks great to me!
Don't forget to take some distance sometimes and consider the model as a whole, and how the effects look like that.
You could just add a couple of small touches of rust to the bollards to add some variation. Maybe the anchor chain could use a little too? Not too much, just a little wash here and there.
I also like how the dust looks on the plates below and next to the anchor chains: nicely lived in!
And I think it adds a lot to the deck too, breaking the 'clean parquet' effect and giving it a more realistic look.
I like how you achied good variation with both hazy areas with soft edges and spotty zones with harder edges.
For further variation on the wooden deck, you can add dark dirty spots too. That is exactly the same as what you did now, but with a very dark brown. That way, you'll have dirt creating contrast in 2 directions: light and dark. Both together offer more variation and effect, but remain sufficiently subtle to remain realistic.