Refinance rental property for stocks

[Trent M.]

Hey guys, first post here. Today I was speaking with a friend about maximizing cash flow on my rental properties and he came up with a BRRR method minus the last R and I thought it seemed like a good idea.

I currently have 2 rental properties and both are paid for.

One is a small house that I have about 15k into and it cashflows about 500 per month.

The other is a quadplex that I have about 70k into and it cash flows between 800 and 1500 per month (one room is an airbnb).

Would it make sense to take a loan against each house for max value (assuming I could get 120k total) and invest it in something like S&P500? Basic math with a 10% return and keeping dividends seems like it would increase cash flow by a few hundred dollars per month just to get a mortgage on them. Am I missing anything here or would this be a good option? Thanks in advance for your opinions/ideas!

One last thing, I'm looking to increase my cash flow more passively than buying another property. I know I would make more with real estate but I would like to get my feet wet with some stocks and could use some guidance.