I thought about doing this myself, but after putting some effort into it I noticed a good 80% of the content on expired domains is garbage, there's a reason the owners let the domains expire and didn't move the content to a new domain. There's a lot of spun content on these expired domains and crappy articles that look like they cost $2, but non the less you can find some good content, personally for me it wasn't worth the time sifting through all the garbage.