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I think its human nature to think more is better.


A good soil will hold water and air.
Soil is as we all know a combination of sand, silt and clay.
I wont go into the ups and downs of sandy soil, clay soil, because we all know the pitfalls of each.

Everyone knows that crops need water, crops need air in the soil too.

A compacted soil will lack oxygen, roots will not be able to take up oxygen, like a heavy clay soil that is over watered, you folks know who you are!


Building soil tilth.
Adding compost and organic matter also helps build soil tilth, why do we need soil tilth? read above.

You can't increase the soil particle size (sand, silt and clay), but you can get the soil particles to form aggregates, by amending the soil. Aggregation of soil particles = soil structure. We constantly amend our soils for more than one reason, but it is different for each gardener and how they have their garden setup.

For instance I have very heavy clay soil and love it, why? Because I built raised hugelkultur beds and used the clay soil in layers with a lot of organic matter, so far so good.

Organic matter is no good to plants until it is broken down by Decomposers, we all know these guys, earthworms, pill bugs, and some are microscopic guys, such as fungi and bacteria.
Organic matter is there to feed these guys which in turn feed the plants (hence feed the soil).


Humus
Humus is not a decomposing organic matter (compost)
I really don't know how to explain it other than it is inorganic leftovers from compost that is needed for mineralization.


Here let Wiki explain it,
Microorganisms decompose a large portion of the soil organic matter into inorganic minerals that the roots of plants can absorb as nutrients. This process is termed "mineralization". In this process, nitrogen (nitrogen cycle) and the other nutrients (nutrient cycle) in the decomposed organic matter are recycled. Depending on the conditions in which the decomposition occurs, a fraction of the organic matter does not mineralize, and instead is transformed by a process called "humification" into concatenations of organic polymers. Because these organic polymers are resistant to the action of microorganisms, they are stable, and constitute humus. This stability implies that humus integrates into the permanent structure of the soil, thereby improving it.
Humification can occur naturally in soil or artificially in the production of compost. Organic matter is humified by a combination of saprotrophic fungi, bacteria, microbes and animals such as earthworms, nematodes, protozoa, and arthropods.


Adding fertilizer
As I said before adding too much fertilizer can increase soil microbes to a point where it can do more harm to the soil than good by breaking down the soil structure too quickly, this works well for short term but is not good practice for long term (building a soil).

Adding too much organic matter, hmm that ones tough, although I feel that this would be difficult, it seem that a few on line sources say otherwise.

My hugel beds are about 10-20 percent Clay soil and everything else is organic matter in the form of logs, sticks, leaves, hay, wood chips, grass clippings, hedge trimmings, cardboard, bio-char, coffee grounds, household garbage, rabbit manure and bedding, plants, compost to mention a few.

I personally don't thing teas and that kind of stuff is needed if you are using compost already, maybe if you were making a tea for houseplants but other than that I feel it's not worth the extra effort.

I think it would be pretty hard to add too much compost or increase microbe activity to a point of diminishing returns without extreme interventions such as chemical fertilizers. As far as too much organic matter, thats a toughie because it's a bit vague and probably a little different for each person, however, I do know this, if you were adding organic matter that is not broken down it will have a (short term) negative affect on the plant life.


Well, that's my 2 cents anyway.