If they manage to derail Kavanaugh's confirmation, it will be a clever, deviously fought victory and, if they also manage to improve their position in the Senate in November, it may make a big difference for various liberal causes in the future. But it's also yet another escalation in the dangerous polarization of American politics, and in that sense it's hardly a cause for celebration.
In the end, adding conservative justices on the SC is less of a threat to progressive values and causes than the other way around, as conservative justices will strike down far-reaching interpretations of the Constitution but don't stop Congress or states from passing progressive laws if they so choose (at least, nowadays they don't - interesting Politico article at the link on the Supreme Court in the 1930s). Donald Trump is a stupefyingly atrocious president and a constant embarrassment to his party and country, but the Gorsuch and Kavanaugh nominations were legitimate and didn't need to be fought tooth and nail like this.
I would agree that the Democrats should have brought the accusations into the open as soon as they heard about them - and they should stop the histrionics about Grassley and the Senate Republicans, who seem to be doing their best under difficult circumstances to give the accusers a chance to testify.