My brother-in-law bought a .223 WSSM at the same time I bought my .243 WSSM. Bass Pro Shop was closing out their M70's and we both got nice rifles for a great price. Amazingly, both have beautiful furniture also. The WSSMs were more of a marketing ploy, IMHO, and are for all practical purposes, wildcats. For the marginal increase in performance (about 300fps for my .243), compared to the increased cost for ammo, one could make a decent argument for WHY. I reload everything I shoot, and brass is higher, and of course you dump a bit more powder in each one, also.
His .223 WSSM doesn't shoot the tight groups that my 700 Rem .223 VS does, but it could be the shooter, too.

He's a few years older than me and doesn't shoot competition. And he's never let me shoot it....
I got my .243wssm to replace my 6MM PPC that had some throat erosion that had effectively taken it to the back seat for competition. Groups were opening up, so I got the wssm. I've never regretted it, but at the 600yd marker, the difference in groups between my standard .243 match gun (Ruger Varmint MK II) and the Win70 .243 WSSM is just splitting hairs.
Bottom line: If you have a reasonably comfortable wallet, a WSSM is fairly unique, and I'm an M70 fan anyway -- so it made sense for me. If you stumble into a good price for one, consider getting it. But know up-front she's going to cost a bit more to feed.