my trezor is still using firmware from about a year ago and working just fine.
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?
You could be fine except for the problem you may get if you want to use it with a new coin only coming in the last updates.
My trezor had 2 year old firmware.