Useless because everyone around you genuinely thinks differently from you? Or useless because said 70+ yo retired asset owners with more means to vote without more than the working class?

Big difference in issue. You can't gerrymander a local bill so those kinds of votes are arguably more important than nationals. And you'd be surprised how big a difference a visit with a few dozen of your peers can make to a townhall meeting. That's something we seem to forget until our backs are truly to a wall.

Only if you are too stubborn to register as the dominant party and vote in the primary.