Tough question without some context to give a succinct answer. Obviously an incremental improvement that will benefit a large group of users can be solicited in a survey. Apps that are "expert systems" delivering knowledge for specific circumstance or user communities may require more thorough engagement, (a first aid app for campers or sailors for instance). Whatever way of gathering use cases or other user suggestions for performance or feature improvement, what is common to all is the need to have a great system for estimating time, sweat and dollars to do it so you don't make false promises and a way to keep everyone focused (a huddle or sharepoint) so that the promises you make are kept.