We attend parties in Carmel Valley and Clairemont. For your basic birthday, you can get away with $10 in Clairemont. But $15-30 in North County is more common. Sometimes close friends go higher, and people who tend to spend money (you know who thye are) do so, but it isn’t really necessary.
Returns are very acceptable, especially when you get duplicates. Not everyone knows what everyone else’s kids like and all parents get this. Because of this, always include a gift receipt so they can return it.
Regifting is a little odd, unless you get duplicates. There is no way your kid will keep the secret, and probably awkward to explain to them why they should. So, only do it if you are OK with everyone knowing.
Have your kids help pick out the presents, too.
If you don’t want 30 new things, in the invitation, let the parents know they can provide a check, made out to a charity in lieu of a gift, if you are so inclined.
I once went in with several other parents and bought 1 large thing. That went over well.
“No wrapping paper” is just wierd. Maybe OK for adults, but half the fun is seeing all those gifts and opening them one-by-one.