If you had put $100 in SPY and just let it run, a starting $100 account would have grown to $1630.80, a 10.32% IRR. Max drawdown was 55.19%.
If you had done 50/50, a starting $100 account would have grown to $1670.81, a 10.42% IRR. Max drawdown was 35.14%.
And if you had used 100% of your account to buy SPY at each close, and sell at each open, your $100 account would have grown to $1699.61, a 10.51% IRR. Max drawdown was only 32.79%. That's right - this is not even holding the SPY at ALL during any day sessions, only buying at the very end and selling at the very beginning. And you indeed come out ahead this way - both more earnings, but, more importantly, a good bit less drawdown.
Do these findings mean that intraday only (scenario 3 - scenario 1) is only worth 59% over 28 years? That's interesting as well. So overnight only in a tax deferred account this strategy looks good.