Do voters turn out for primaries where there are no contested races or where everything has been “decided” prior to the vote? No. Do voters show up when races have multiple candidates vying for the same spot and people have a chance to alter the outcome. Absolutely!
Case in point is here in New Mexico. We have been on a downward spiral of ever decreasing voter turnout cycle over cycle. That all changed and in a big way this 2016 primary cycle. Why? Both macro races and micro races had some hot contests, especially on the Democratic Party side. Democratic turnout was 37% statewide compared to 27% for the Republicans.
Macro was the Clinton vs Sanders Presidential race. Driven by supporters adamant to be heard, the Sanders faction showed up in numbers large enough to take the City of Albuquerque and Bernalillo County. Wins were also posted in Taos, Clovis, and Portales and their associated counties. On top of that, Sander came within 6 votes of besting Sec. Clinton in Grant County (Silver City) and within 21 votes in Los Alamos County. Close contests were had in two other large counties, Sandoval and Santa Fe.
Micro came from localized races that were very close. In those counties, neighborhoods, etc. find themselves attracting more than the usual attention to vote. In New Mexico this year, the perfect storm of this occurred on the Democratic side in the South Valley of Bernalillo County, Several areas of Doña Ana county, and up in the north central counties of New Mexico. Many of these races had more than two candidates AND the outcomes were decidedly close. Several of these contests happened in places where the Sanders coalition was weak. So, voters outside the Macro group showed up as well.
Democracy works best when people get in the game, run for office, and vote. Patries themselves sometimes try to discourage primary contests, especially against incumbent, but overall, the voters appreciate having choices.