Let me say it again, prioritize and focus.
This is something I am addressing on my current product... making sure the team focuses on the core issues, the product basics, and getting those right before solving the 10% problems or the fringe problems.
This sounds so basic, but it is a consistent challenge that a leader faces: how do you keep your team focused on the high priorities and what's important, especially if those two are not sexy enough?
What I do is acknowledge that those other issues are important, and are relevant, they just do not rank in priority relative to other features. For example, Amazon.com is a great retail site with lots of features, but none of those features (product recommendations, shipment tracking, cancelling orders, gift options, wishlists) would be relevant without the basics: placing an order, processing payment, emailing confirmation to the customer. While that sounds obvious, and it is obvious, it is still true that many. Take a bunch of Amazon engineers, ask them to build an e-commerce site from scratch, and I guarantee the first questions and focus would be around shipping, promotions, recommendations, split orders, etc. The discussion would not start around the basics.
In addition to acknowledging those fringe features, I document them and put them on a priority board. Acknowledging the importance, and selling the idea that there are simply more important things to focus on, is an important step when these issues come up. In addition, it gives a great respite for engineers that need a break from the here and now and want to spend a short amount of time working on something new - there's a board already set up to pull those ideas from.
None of this is rocket science, none of this is new. That said, I do see teams managed that do not execute in this manner; they may have these tools, but they are not enforcing this as part of culture and execution. That's what needs to change. It will be your biggest challenge in product development.