Yes, I would recommend upgrading to Big Sur if for no other reason than to know that I have used the hardware to its greatest potential under macOS.
There were some major architectural changes made with the release of macOS 10.15 Catalina, and Big Sur stepped forward with what I would call the modernization of the OS.
Upgrading to Big Sur will mean that your older 32-bit apps & drivers will no longer work. They must also be updated or replaced. You can use the free utility Go64 app from St. Claire Software to check which of your current apps would be affected.
The upgrade would open the door to more modern and secure internet apps and connections and let you eke out a wee bit more productive use.
Of course you know that Mac is twelve (!) years old now and long regarded as obsolete, so it has a short span of usefulness before it.
Several of our veteran friends in the Community would recommend ditching macOS altogether on that hardware and suggest installing a flavor of Linux, specifically Linux Mint. Linux could give the computer new life beyond what is available under the limitations of macOS.