You booked that flight because of the price (otherwise you would have booked the later SNA-LAX flight). So IMO that is the flight you should take, unless you want to pay the change fee.

As others have stated, pricing is not the same from both airports all the time.

I agree lying about being stuck in traffic isn't right, but telling them why you want to do it, won't yield the desired result either. In any case you may be able to do it, and you may not, but you run the risk of maybe getting away with it, or paying the $100 fee, or even worse paying the fare difference. So if you are a gambler take the risk, if not don't. Without a doubt there is a risk and the price or problems you could encounter probably aren't worth a few hours.

Personally I wouldn't eliminate anything other than the last segment (which I have done many times on the return LAX-SNA). You will not get the 500 miles if you don't fly unless UA provides ground transportation (which this is not the case).

As far as flying out of SNA they hold the brakes, rev up, pop the brakes, take off steeper than normal, get to 800 ft and pull back on the throttle. Depending on where you are sitting you may think someone turned off the ignition as it goes from a steeper than normal climb, to more level rather quickly. Then they follow the water out left and right to try to avoid flying over houses. It isn't a problem or scary it is just different and thus most pilots warn everyone so the passenger doesn't wonder what is happening.