Actually if past trends are anything to go by, socket 2011-3 motherboards aftermarket prices will be pretty good. Just look at what decent X58/X79 boards go for used, the OEM ones can be pretty cheap, but any decent ones cost a decent bit used.
Agreed, the enthusiast platform boards in general have a good history of holding their value for quite a while and having upgrade options for a good long bit down the road. There are folks that are just now upgrading from X58 platform boards and some folks still sticking with them by upgrading to a Xeon with 6 cores off eBay for all of $100 and getting a decent performance increase out of it.