Yes, open primaries improve voter choice by giving voters more candidates to pick from. This is a positive thing, and keeps the choice for voters more open. Having a closed primary only allows voters to vote for a handful of candidates, and this is not a positive for voter choice.
Open primaries are necessary for a truly Democratic nation to thrive. Democracy is about choice, and by not offering voters the chance to freely choose in an open environment many political decisions may be made behind closed doors. An open primary policy would allow voters to choose their representatives with more confidence and those representatives might in turn be held more accountable by those who voted for them.