1. Not showing up to vote can be a positive act, but it most likely is perceived as apathy. Note that in Eretz Yisrael the non-zionist hareidim do not vote, which has zero impact on the political process (an alternative used by Irish nationalists 100 years ago was to participate in elections, win seats, and then refuse to take the require oath of loyalty).
2. In America, one votes for many offices at the same time, so a “blank” ballot for president is counted as a blank (since they know how many voted altogether, and how many blanks in any given race).
3. If you are a committed neo-con, you no longer have a horse in the race. However on economic issues, Johnson is a real alternative. On “social” issues all candidates are probably too “liberal” (“permissive”) for our tastes, but a libertarian ideology is more likely to leave us alone.