not about leadership, since politically the opposite party is supposed to stay out of the other parties leadership choices.

But I would write to them (without saying you're x party) to tell them you care about accountability, affordablility and in general what you're in support of or against. like someone else mentioned you'll get a canned response but that tally tells them a bit more about what their constituents want (whether they listen is dependent on how threatened they feel when it comes to re-election).