Most of these aren’t really the perks, but other things that you can potentially talk to your parents about.
Taking the MSF course is a good start to convincing parents. It shows that you want to have a responsible start to your riding career, which means that you’ll be more likely to be a responsible rider in general. (And telling your parents that taking the MSF reduces your chances of getting in a wreck by 50% or so isn’t bad either).
Unless your parents really hate motorcycles, why not see if they want to take the MSF course with you. They can see for themselves that you’re being responsible and that “motorcycle” is not synonymous with “deathtrap.”
The fact that you’re looking at a 250 means that you’re not looking for the fastest bike on the road so that you can pop wheelies at 100 mph. You’re looking at a good beginner bike, which is another responsible move.
As Munch mentioned, the downsides are that you don’t get the same protection that you get in a cage. You’re also less visible than in a larger vehicle. The weather can be a serious problem if it’s your only means of transportation, although probably less so in California than here in Massachusetts.