I’ve personally always liked firebreak sprints. Every so often (3-4 times a year) in between other large pieces of work, take a week and give the developers free reign to individually fix the things they think are most important but never seem to get prioritised.
Yes, it talks to a disconnect between product and engineering, but working on that relationship at the same time doesn’t mean that both aren’t worth doing.
The Shape Up model (originally from Basecamp) builds in a 2-week "cool down" period after every 6-week "build new stuff" period. We further designate one of those weeks as a "bug blitz." That 1-2 weeks in every 8 cadence really helps encourage fixes not just new features.