The extension table attaches to the rails of the fence. It is not
necessary to attach it to the wing. Getting the thing level with the
wing on the other hand is a pain. If it is not completely right the
fence will clank every time it goes over the bump and you have to take
the fence guide rail off to fix it.

You definitely want the cast iron wing, whether you want the extension
table as anything more than stiffner for the fence rails is another
issue. As far as I can make out the only use for the extension table is
when dealling with really big chunks of plywood. I use a circular saw
for those cuts.

The wing on the other hand is pretty useful because it gives you
another 12" width to what is almost certainly the largest surface area
in your shop that is really flat.