Since your 401(k) is with Fidelity, does it allow you to open a BrokerageLink account? That's Fidelity's brand name for optional self-directed brokerage accounts within workplace plans that they run, but not all of the plans they run allow BrokerageLink accounts. I'm just asking because it seems to me that with your level of technical knowhow and the systems you've set up, you might prosper more with the (relative) freedom of a BrokerageLink account than having to be at the mercy of a limited menu of mutual funds, the contents of which can be changed without your consent.

By the way, is that S&P 500 fund using the dividends to issue you additional shares of the fund? The tax code requires mutual funds to pass all net income to fund-holders, so if the fund isn't just sending you the dividends, then they must be "giving" them to you in some other way, and the only other way I can think of is for them to use the dividends to issue you additional shares of their fund, like a DRIP. I'm with you; I too would rather have the discretion to reinvest my dividends as I see fit!