I upgraded to a steel rod with increased spring rate for my G20 (10mm) to better handle full pressure loads.
My other Glocks all run great with the factory recoil setup. Never a problem.
So, worth the effort and cost if you have a specific performance issue that you're trying to address, like improving consistency under high-pressure loads. Or if you just want to experiment.
But for a stock Glock, in normal use, I doubt you'll see an improvement that justifies the cost.