I think that's a great suggestion for companies that can work out a way to do it! I think probably particularly useful for community theatre companies and privately-held ones, where budgets are particularly small and the labor put into the auctioning process results in a comparatively large return.

A lot of the theatres i've worked for have had a lot of bureaucratic red tape to consider when it comes to thinning stock, though, depending on whether they were state-sponsored, in residence at a university, a particular scale of non-profit, etc. (It's not to say it couldn't be done, of course.)

For example, at my current employer, we couldn't eBay any of our stock because it's technically not the property of the company, but the property of the university; in order to "liquidate" any of our stock, we have to send it to the Surplus department, where it's sold off through state-approved channels and the revenue goes through a million different pipelines, usually not back into our own coffers. We can donate things to charities or other state-sponsored or -recognized organizations with much less paperwork and effort, though.