Personally, if it was me, I'd update it.
As with most things, there's going to be two different views. The "If it ain't broke, don't fix it" which blends with the "Don't update, they're going to make your bike slower and take features away" view.
The majority of changes in a firmware updates fix tiny software problems. The "If it ain't broke" is actually "You just don't know it's broke".
They're constantly testing and refining. Improving the efficiency and range, improving how the motor responds and probably most importantly, improving the reliability by making it smoother in how it engages and delivers power - which is in everyones interest. The sooner you make a change which will improve longevity, the longer it will last !
There was one massive boob, the walk mode downgrade, which was added to the base firmware by Brose. Fortunate Brose and Spesh worked together on this one and came up with a solution which was part of the first OTA update.
On the flip side, one of the most welcome firmware upgrades was the change on the 1.3 motors from 16amps to 20amps. So just like that, you got a 25% more powerful bike than you had the day before.