Sounds like it is an important integral part of your complicated setup.
Definietly give it a go by shitting it down and replacing the Pi, but I have to ask, why replace the Pi3?
Is there a good reason to?
ie are you chasing more speed or any other reason to replace the Pi3 other than the Pi4 is newer?
Usually if you have something working in a complicated setup like it sounds like you have, you leave it alone without a really good reason to change it.
I have a couple of systems like this.
Sure I could replace the Pi3’s with Pi4’s, but I dont actually have a need for it.
As a heads up, you are periodically backing up the Pi3 disk image arent you?
Pi SD cards can and do dies regularly, and there is nothing worse that losing your entire project to a dodgy SD card.
