Some ideas.

1. On the survey, could you reduce the effort required? For example, a pulse survey with a smaller sample, held more often? Or an in-context survey where people who have *just* finished using your data product are asked if they e.g. found what they were looking for? Maybe re-read CJ's "Surveys that Work" for inspiration?

2. Definitely don't take responsibility for measuring quantity or quality of decisions that get made :) - as you say, you're enabling the decision-making. You can only take the horse to water...

3. Maybe you *can* do more to identify the different types of decisions that need to be made by different audiences, and what data is needed by them to make those decisions well? Could fit with your aim for distributed responsibility for data too - e.g. Heads of Professions should be able to tell you what sort of decisions and underpinning data is used by each of their professions in data-mature organisations. Sounds like you're working on that for product people already.