As you can gather by my SD Tag I love the WSM range of calibers and definately wouldn't go back to standard chamberings. I've taken deer with both 300 and 270wsm and have never had a problem with "the lighter animals" with velocities over 3000fps.
Winchester developed the wsm range to fill a gap in the market, they were looking for a cartridge that would produce the same ballistic and terminal performance as the standard chamberings but in a shorter action, theoretically making a quicker and easier cycling round. They chose the .404 jefferies as the donor case as it's wider than the standard 300wm and so can hold the same volume of powder, but in a shorter case. In doing so and altering the shoulder angle, Winchester developed a range of cartridges that are far more effiecient than the standard calibers, they even pushed the idea further with their WSSM loadings in .223 and .243 both of which make the standard rounds look like rimfires. After the orriginal offerings of .270 and 300 and their subsequent success they added others such as .25 and 7mm.
Unfortunately the wsm's have never really caught on as much in the UK as other countries, this drove ammo prices up making them expensive guns for people who don't reload and pushed the second hand value down, which is a pity as they are extremely versatile chamberings. There is no shortage of brass as most of the major brands produce brass for them plus nearly all of the major rifle manufacturers list wsm calibers.
Al, if the rifles you have seen are clean and you are prepared to reload for them my advise would be to go for it, you'll get more rifle for your money.
Ade