Welcome and thank you too
If your needs versus wants require an new or newer computer to avail yourself of the newer or newest versions of macOS - Yes get a new or newer computer
If as you say the machine is in excellent working condition and to reduce your costs >>
Explore the Apple Trade-In Process where the Value of the exiting device could be used against the cost of a new Apple Computer, iPhone or iPad
Notation - Some devices and depending on the computers age may have little to no value at Trade In time.
But at least the device will not arrive to the Land Fill Site and be recycled in a responsible way by Apple
Or Shop Refurbished Apple computers at an Apple Reduced Cost
Have used both previously and have been satisfied each time.