In a conventional approach, the maturity assessment model is based on elements such as specific goals and objectives of the organization, clear and measurable levels of maturity, as well as the scope of the model itself. Should its success also be based on a high response rate, actionable and meaningful insights, or is there any success matrix that may be recommended?

Clear metrics for ROI and VOI need to be established. As stated above, actionable and meaningful insights are a must, but just as important is the actual changes to operations that are implemented from those insights. I would also include benchmarking and the use of best practices as part of the matrix.

What about IT risk management frameworks like NIST? Those will usually give you actionable and meaningful insights after your risk assessment!

Target the main stakeholders - define the list from those in senior positions, along with the people who have the most experience in the department first.  If you're lucky enough, you might be able to ask the opinion of those who has the least experience too, but this can often dilute the results.

You need a mix of people from different teams, backgrounds and roles.

I defined the criteria from my own experience, industry best practise along with the Strategy.

Choosing the right participants. It is important to determine the “goodness of fit.” A poor fit of the participants often results in misleading evaluations, and further affects the direction/ decision making when developing the corresponding improvements measures 

As said, results are the key to keep the success going. Measuring it might differ on the expectations of either quantitative or qualitative approach that the venture is expecting.