If they are running extras and you're not, they'll likely be in a different division. Let them go but ask them why they needed to pass you so damn close.
If you're not flying a kite, and someone in your race is coming up to pass you with a kite, you are racing, and you do what you must, cover, luff, whatever.
If they're in a different race, and they basically come up behind you, steal all your wind and slow you down, and crap all over your parade this might be considered unsporting behaviour and you might protest them out of THIER race, under some rule or other. Maybe they are sailing interference for a friend further back who is actually in your race?
Additionally, if they're not in your race, racing rules do not apply and colregs do. As passing boat, they have to keep clear etc. etc.
Sail your race, race against your competitors.
Starting no extras first or not? Totally depends on the start, upwind/downwind etc.
I'm usually on smaller boats, extras or not, and it's nice to get away a bit before and be a bit spread out then have the bigger faster boats come through you. Even though they're not in your division, it's demoralising from the start to feel like you're chasing a bunch of faster boats.
It depends on the race, but in a passage race where there's a big party afterwards, on a small boat if can be crap right from the get go if you're already starting last, almost as if you and your division are an afterthought to the rockstar boats ahead of you. When they p¨ss off over the horizon almost before you even start, you know that they'll be starting the party before you get to North Head.
But as some have noted, it can be that there's precious little in it between the extras and non-extras.