Would bark fines improve raised bed?

[RayR]

Agreed Dice, organic matter is best placed on top of the soil. That's how nature over time creates rich soils below.
Compost mulches or even partially composted mulches are probably the quickest way to achieve long lasting results for gardeners who plant in soil because they are already rich in microbial life that is releasing nutrients and compounds like humic acids whose benefits reach deep into the soil. You mentioned "soil aggregation" earlier, which I think is very important point because many people I know who garden don't grasp how important it is to create an environment for soil microbes to flourish at the surface of the soil.
I've noticed myself that in my beds that have had organic matter simply tilled into my heavy clay soil to fluff it up, if there were benefits for that season, those benefits didn't last long. But those beds that were mulched with organic matter had soil structure that was improved even the next season.

[dice]

There is also the question of root-knot nematodes. Trees, shrubs, and
perennials that are part of a permanent landscape installation are not
likely to have problems with nematodes, even if they are normally present
in local soils, but most tomato cultivars and many other vegetables do
not have any resistance to nematode root damage. High levels of organic
matter make life difficult for the nematodes, and so one would need to
adjust "optimum" levels of organic matter in garden soil upward in areas
where root-knot nematodes are found in the native soil.

Bark may add organic matter, but it is not high in nutrients, so you are
not likely to get nutrient overload mixing it into a raised bed. I would not
really expect it from adding generous amounts of compost, either,
especially if it is added as mulch on top of the soil. If adding nutrient rich
manures, on the other hand, a soil test first can help prevent problems
that result from nutrients accumulating in the soil in excess of what
the plants use each year.