According to the advert (http://wayfarer.org.uk/index.php?option=com_sobi2&sobi2Task=sobi2Details&catid=3&sobi2Id=146&Itemid=234) W8145 is a MkII. The self-bailers fitted to a boat like this are designed only for use whilst underway. A ‘self draining’ boat, on the other hand, has its floor raised above water level so that rain water can flow out whilst the boat is on a mooring. Obviously this raised floor must be watertight, so this creates a sealed buoyancy chamber under the floor. The Wayfarer World has the same arrangement.
The most often cited problem with this is that the boat can tend to invert after a capsize, due to the location of the buoyancy. However in my limited experience most Wayfarers will have some tendency to invert anyway so I don’t think it makes that big a difference. The downside of a more conventional boat, like the MkII you are looking at, is that if you leave it on a mooring you will have to visit it occasionally to bail out rain water. Again this isn’t usually a big problem unless you are planning on leaving the baot unattended for weeks on end.
W8145 looks like a nice boat, good luck!