suggest reading this
https://www.sipc.org/for-investors/what-sipc-protects
what happens if the brokerage firm 'cooks the books' and sells your stock without your knowledge, but gives you a statement saying that the stock is really there? THAT is where SIPC comes into play.
Rather than opening up multiple accounts, go with a reputable firm (large, well known), that reputation is worth more than the SIPC insurance in my view.
