Hi nannolo!
You put an interesting and old question, many modellers debate this during the years.
In my life I came across restoration of the Ansaldo A.1 Balilla held in Bergamo, I remember well that woodgrain of the single wooden sheet that covering fuselage side disappeared under the coat of dark protective coating. When you stand up 2 metres away from the fuselage you can't see woodgrain.
So, in my opinion representing woodgrain in scale is a mistake. If you take "scaled" woodgrain (decals, etched etc.) and give them a 1:1 reality, I think there is no that kind of wood in nature.
On the other side, depends on the nature of the paint that mechanics used. Black crosses under red paint are visible, also in 1:1 you need 2/3 hands of paint to cover black with red. Albatros used a light combination of wood/protective covering so, and this will be my way if I will build one, no woodgrain visible under Jasta 11 red.
Sometimes I think that modelling was crossed with "artistic way of modelling" and visible woodgrains is one of the case. Of course, everyone of us can decide in freedom what "style" is good for his modelling, this is "my two cents".
Ciao!
Roberto