I guess it depends on your current age and income. If you’re in the 25% tax bracket or higher, figuring out how to reduce your taxable investments is important.
If your company supports it, look into after tax 401k. My last company did – I only put in 25% – wish I had maxed it out as my current company does not. Now I only have the backdoor Roth option.

You could pay off your mortgage since there is pretty much no tax benefit now with the new tax law, but your rates are pretty low. Probably better off to invest.

One of the problems of real estate investing in CA is the high prices and low cap rates, not to mention the rental landlord rules. Personally, I think places outside of CA provide better cash flow, but CA does usually have better long term appreciation – just might have to wait a while for the next up cycle.
I’m also invested in Realtyshares, which does partial ownership of real estate (8-16% returns), but you have to be an accredited investor. It’s a nice balance to actually being the landlord and having property to manage – and not having to put 25% down for investment property.