This idea has already been proposed in response to one of many questions about the size of the close vote queue on Stack Overflow. So here it is again, as a separate feature request:
Reset the close vote queue.
Pick a date, and mark all the close-votes that are earlier than that date as "hidden", and only show the newest close votes. At the point of enacting this, and picking the date to be "now", the queue size should go down to almost zero.
Watch the size of the queue for a week or two. If it has grown far beyond zero, then this experiment didn't work, and you can unhide the old questions and return to the status ante bellum.
But if the queue size does remain near zero, then it means that people are more motivated to contribute where they feel they can make a large relative impact. Achieving "zero" is a feel-good goal, while achieving "91225 (down from 91240)" doesn't feel that big of a deal. And if the experiment does work and we manage to keep up with a fresh queue, then we can slowly layer old questions into the mix, money-laundering style. Nobody will ever notice :-)
Let me offer another angle on this suggestion.
I want to analyse the claim that there is a motivational difference between a full and an empty queue. Specifically, the claim is that people are more motivated to work on a small queue, for psychological reasons. It feels like you're making a greater impact in making a small problem resolved than in making a large problem a tiny bit less large.
I have no proof that this effect exists on Stack Overflow, only circumstantial evidence coming from the observation that all the other queues consistently go back to zero regularly.
We could obtain further support for or against this claim by looking at historic numbers of queue throughput (which I'd like to see, if anyone can pull this data out); and/or we can run an experiment. Either way, I believe it would be valuable to find out for sure if there are psychological measures that would improve user engagement that we're currently leaving on the table. I'd be perfectly happy to find out that nothing of this sort is the case, but I'd like to know what we know.