Do you mind if I make a few gentle corrections? I'm not trying to be that guy on the Internet who starts a flamewar, but point 1 needs clarification and point 2 is just outright false.
Passing surges into the power supply is expensive, as even if the power supply protects your computer as a whole from a surge, it will likely blow a capacitor in the meantime and render it unusable. That's why it's a good idea to use a power strip with surge protection to plug in your PC. Overpower (shutting down when the power supply goes past its limit) and overtemp (shutting down when the power supply gets too hot) protections are also fairly important.
Let's use a hypothetical of a high-quality PSU rated for 500W being run at exactly its rating of 500W. Let's say at 100% that this PSU is exactly 80% efficient. This doesn't mean that it can only draw 400W, or 80% of its spec. It is rated for 500W after all. It means that when 500W is being fed to the system, it draws about 625W at the wall.
That all being said, power supplies are generally not designed to be run at 100% of their capacity all the time and will lose some of their ability to properly feed power to your system over time, especially when stressed so hard. Not only that, not all PSUs are created equal, and some no-name ones say they're rated for 500W but in actuality can't draw more than like 350W. (See jonnyguru's "Death of a Gutless Wonder" series.) That's why it's generally a good idea to give yourself a bit of a buffer - 30% isn't a bad guide in general, though for a good PSU you can probably get away with 15 to 20%.