Unless software 'times out', the fact macOS may not support later versions than the one in use matters very little either. This is why for some people it is still possible to use G5/G4/G3/68k Macs for productive work, even now.
All of which means that if it were me, I would be happy to stick with what I already have if it still works for me the way I want it to, and still gives the results I need. But, if I were to find it lagging, particularly in being able to deliver results in a timely fashion through performance degradation or software restrictions, I would look to upgrade, based on the realization that the time I was losing to poor performance costs money, and that a new system would potentially pay for itself reasonably quickly as a result.