Ask HN: Is it time to engage less with our prospective customers?

We launched a landing page in the beginning of the year and we have diligently followed up with every person who has taken an interest in our product (which is still under development and has not launched yet). We have learned a tremendous amount from the feedback we have been getting and I am happy with the performance of the campaign (we have a conversion rate of 20 percent). However, we have reached the point where we are not not learning anything new from this process and it is consuming resources that we would prefer to spend on product development.

What would you do in this situation? Stop engaging new users who sign up or simply provide lower-quality feedback? (People send us their Excel spreadsheets to learn if they are good candidates for conversion to apps -- which is what the product does -- and analyzing these spreadsheets is time-consuming.)

I would like to think that engaging with users this early has the added benefit of creating solid beta testers down the road when our prototype is ready, but I am concerned about not being able to devote more time to product development. Thoughts?