is there any REAL reason to update the firmware, or is it recommended to leave it be and avoid the risks and complications of backing-up/offloading the coins, formatting, then moving everything back on again?
... another thing to note here is that the 'backing up' of trezor is no more than writing down the seed phrase.
I like to think of trezor as more of an empty vessel that generates keys on demand rather than a key container. You can have multiple wallets with different seed phrases and, depending on the purpose at the time, wipe the trezor and load up the seed phrase you currently need. If you get used to regularly wiping the trezor and loading new seeds on securely it makes the trezor more versatile in what it can accomplish.