Turnout in local elections is very low. That doesn't make you meaningless. If you vote in local elections, it makes you more meaningful, because your vote has more influence.

It depends how you define low. The US has low voter turnout by total population (~55%), but very high turnout by percentage of voters registered. Many states have artificial obstacles in place to suppress registration and turnout. Other states like Oregon and Washington have implemented mail-in ballot voting and automatic registration which makes voting more accessible, and have higher turnout (72%). It's certainly not meaningless.