Dielectric grease is thicker than 205g0, and IME it works better than 205g0 at removing stab rattle/other noises. However, I've noticed that because it's thicker than 205g0, it can make stabilized keys feel slightly different than 1u keys, although it seems to be more noticeable on linears versus tactiles/clickies. It's not a big difference, so I usually go with dielectric grease for stabs

I've never had to add extra grease to a stab, even on keebs I've had for years. If I felt like a stab needed extra grease, I'd probably just remove it, clean it up, and re-apply lube. It seems like the point of using a syringe to lube stabs is that it's more convenient on non-hotswap boards so you don't have to do any desoldering to remove the stabs