I see a couple of wins here. A rally or two is bound to pull out the remaining Republicans and Independents, resulting in a massive turnout and scaring the crap out of the Democrats, so:
1) The Democrats panic, sucking money in to a "safe" state that would otherwise have been used against Republicans elsewhere.
2) The rallies would energize the "forgotten voter" (Hey! They remembered us!"). President Trump has no chance to win the state, but out-of-the-closet voters might put some down-ballot Republican representative in Congress.
Agreed! #2 was already mentioned after my post in the thread. But making the Dems spend in CA is another upside.
Good points all.