the fans may be useful as system fans, or if you build a new system and are able to transfer your current cooler. Personally, I don't ever throw anything out, I can either find someone to buy it, or I just keep it. This would probably be in the keep category.
You should stack them together and make a SUPER HEATSINK that would be kick ass. You could have the fans like sandwiched in between than use thermal paste on each heatsink or something. Dunno. Or just stack them than super glue