In my experience, LTS (Long-Term Support) versions of SonarQube fit your description: critical bug-fixes are backported while no enhancements (features) are supplied.
In my organization, we stayed on the LTS for SonarQube 5.6.x instead of opting for the “Latest” version (6.x) because 6.x lacked some enterprise features we needed (support of the governance plugin) until the next LTS (6.7) was released. The guiding philosophy for our group responsible for maintaining ALM tools is usually to stay on the latest version, but we couldn’t give up those governance features.
When 7.0 (Latest) was released, we opted to upgrade since those enterprise features persisted (and our contacts at SonarSource ensured us that kind of feature removal was a one-off event we shouldn’t worry about). Our experience has been positive, and upgrades are much more painless since we aren’t introducing large amounts of changes to users once a year, but instead incremental changes (and awesome new features) every month or two. I have even more faith in running Latest since that’s what SonarCloud, SonarQube’s SaaS offering runs.