Voting is the minimum. If voting isn't enough (I didn't think it is) then do more. Go knock on doors for the candidate that you like. There are a million ways to participate in democracy. The answer to a flawed system isn't to do less.
These "both choices bad. Better to not vote" people really don't make any kind of sense to me.
Image being unhealthy and saying "it's going to take more than a 20 minute walk once a week to get in shape. Better not even do that then cuz what would be the point?"