Dae tries to keep things as backwards compatible as possible. Anki 2.0 was able to sync for a long time after Anki 2.1 arrived, but eventually support had to be dropped. The GUI changes are no big matter and are not a reason not to update. If you don’t need the newest and fanciest Anki, I’d rather recommend you sticking to the release cycles a few add-on developers have decided to adapt, such as lovac42 and Migaku (former MIA):
This addon follows a six month development cycle to avoid problems introduced to addons due to the constant fluctuations made to the Anki API. I do not want to stop maintaining these personal projects, but it is extremely taxing on a developer’s schedule when we have other deadlines and obligations. Hopefully, adopting a six month development cycle following the MIA Team’s example could solve some of these issues.
Current Target and Cycle Details:
Anki Version: 2.1.22 (Windows and Linux), 2.1.23 (macOS)
Start Date: April 2020
Next Cycle Start Date: October 2020
So long story short: as long as you are on any 2.1 version and the add-ons you need are compatible, no real need to update. But also no real reason not to.