There is absolutely no reason anyone should need to convince someone who is/isn't using valve caps or stem nuts to change their ways. Regarding valve caps I've not seen any significant difference myself in 40+ years of riding presta. As for stems, it depends on your usage - pumping technique for one but more importantly how well you keep your tires aired. If you aren't conscientious and allow them to get low on a regular basis the tube can creep. If you have a tight valve nut the tube can eventually stretch enough at the base of the stemp to cause a crescent shaped tear. Without a valve nut you will see the valve start to tilt at an angle, letting you know you are not keeping the tires aired and that you need to reinstall the tube properly.