I dunno.... Buydomains had Fours.com listedfor a while @ $800'ish - I think it was an iREIT name... It seemed like kind of a good deal at the time, which is why I remember it, but it's hard to peg down value on names like this since they have so little inherent use and generally, only appeal to domain 'collectors'.
If there is some ancillary meaning (like you explained, in sport, or whatever) then there will probably be someone out there who will want it.