It's a bit the dilemma, that knowledgable individuals with a sharing and giving attitude are more likely to get over-consulted, as persons who first ask "what is in it for me?" before they share their knowledge.

Consulting is just one form of engaging. If we are over-consulting with a particular group, possibly the question we should be asking is how well have we identify the stakeholders for the issue we want to consult on. The correct identification of who the relevant stakeholders are will always be key for gauranteeing the quality of the outcome from any stakeholder engagement process.

Yes, we are in danger of over-consulting the same group, and doing a very bad job of co-generating value from the ones that we do engage with.

Yes, over consulting with same group without creating returns/tangible value leads to lack of interest and makes stakeholder engagement a routine exercise without meaningful outcomes.

Yes, and as someone who was over consulted and saw little social or personal value from it, I have largely withdrawn from the networks and see no downsides!

yes
and one downside is that the stakeholders who descide to stay IN the groups or to keep responding (for diverse reasons) are largely the same persons thus reducing the diversity in answers and points of view.

Forgive me if I misunderstand the question. I hear in it an inquiry into whether the community actively promoting new values in business and the economy that are truly well adapted to the new realities of life in the 21st Century spend too much time talking to the same people, being those who already do see the value of valuing new values, so that the movement is not really moving outside this (smallish?) circle of the already convinced. It is stalled.
If that is the question, I see in it a hopeful sign that the community is gradually starting to become open to the possibility that talking about the values we need and want to be valuing is a critically important first step in a two step process for actually changing the values we do value. The second step is empowerment.
Moving to the second step requires creating by design a new social structure of value recognizing frameworks, processes, places and people that is adaptively evolved to recognize the values we need and want to be valuing today.
Consider the stakeholder currently living within the popular Wall Street social structure for recognizing value in enterprise through investment decision-making as speculation on movements in the market clearing prices for securities derived from Main Street enterprises traded as commodities in markets for setting on always-available market clearing price.
In those markets, we all have a voice. Those markets are authentically open and inclusive. Also, our voices can only be heard in those markets if we are saying either "buy" or "sell". Those are the values that move those markets. All other values are OK, but no other values have any impact.
This is not a moral choice. It is how the social structure of speculation is designed to work. Its frameworks, processes, places and people are all designed to recognize the value of the always-available market clearing price. Values that restrict the availability of a market clearing price are not valued in that social structure, precisely because that social structure is purpose-built to always deliver an instantly available market clearing price.
Think of the Wall Street social structure as a technology, like a car. If we want to fly, we cannot just bolt wings on a car, and expect to get it airborne. We have to take out a clean sheet of paper and build by design an airplane.
Whether you own the rights to buy or sell shares in the car (as an investor in the Wall Street social structure of speculation on market clearing price, such as a pension fund), or are just driving the car (as an executive running a company financed through the Wall Street social structure), you cannot be expected to get that car to fly. The physics are against you there.
If we want to be recongizing other values in addition to the values that set an always-available market clearing price, then we have to move into a social structure of frameworks, processes, places and people that is designed to value those additional values that we also want to be valuing.
We know well now what the new values we need and want to be valuing are. How shall we design the right social structure that will empower us, truly and authentically, to value those values?