There seems to be a significant asymmetry between the efforts required in closing questions versus reopening them. As a partial remedy, I propose a policy to balance this: moderators reopen the borderline questions with less hesitation, without waiting for the 5 reopen votes, if there is a reasonable request in meta for the question. (Edit: A more systematic and fair procedure for this could be like the one suggested by Bill Dubuque in his comment: "close votes could be up/down in comments maintained by moderators, and closure could be done by mods when a community agreed upon differential is reached." )
In particular I would like to see cases like these avoided: user comes to meta, asks for reopening a question, 4 reopen votes are collected, but eventually the votes expire before the question gets reopened. A moderator could have intervened here and just reopened it. There is already a bias towards staying closed, so this sort of unilateral moderator action would only help to balance the situation. If some user thinks s/he has a good answer for some question, I don't think it helps the site to stop him/her by keeping the question closed.
As far as I know, a single moderator vote is enough for a question to be reopened, or closed. There are many cases when a moderator has closed a question unilaterally, but very few cases when they reopened one, before waiting for 5 votes.