Extracurricular activities aren't essentials. They're typically considered entertainment and while it's discretionary, from experience they don't award these costs.
As for college tuition - unless the original judgment addresses these expenses or unless you & the NCP stipulated to have CS continue to cover college expenses, there is no obligation to pay support in CA beyond the age of majority. It's purely voluntary on the part of the obligee parent to decide whether or not to agree to pay for college.
California CS guidelines provide for a hardship deduction for additional kids, but since you've each had another child, those deductions will cancel each other out.
Re: the braces - does your order provide for the NCP to cover 1/2 of unreimbursed medical & dental? If not, you could request this.
Courts don't award an increase in support based upon the age of the child - it's based on income & tax rates.
A $50 increase in insurance doesn't constitute an extraordinary change in circumstances.
You could go in for a modification based on an increase in salary and see what happens, but if the increase is going to be minimal it probably isn't worth the time, aggravation and attorney fees. You can go to
www.xspouse.com and download the CS demo to run the numbers.
Honestly, unless NCP is making a whole helluva lot more money and you've had a decrease in your income, it probably won't be worth it. In fact, if you make more money and NCP's income hasn't changed, you could even be looking at a reduction.
That's a decision that you have to make - cost / benefit analysis and all.