I have two apps that are pretty popular, but I hadn't updated either in at least a year. I just updated one a couple weeks ago. I can say it was a struggle just for some minor changes. If you have apps that are worth continuing, you have to budget some time to keep them updated. The technical debt of not updating will grow your procrastination muscles exponentially!
A neglected app ... will also create a lot of technical debt that only becomes harder to fix as time passes.
Staying Competitive With App Updates by Kyle Richter