As I recall: The danger of a lightened recoil spring occurs when combined with an extra power striker spring. The trigger pull could possibly push the slide out of battery after the safety plunger has depressed to allow the gun to fire out of battery.
I have a Generation 4 35. I swap back and forth between 40 and 9mm. When shooting 9mm I use a Model 34 spring and a model 34 barrel. I've had no issues at all.