I understand that an unsupported spade rudder might have less drag, but on boats like these, with cruising speeds well under 10 knots, that difference would be negligible. The strut-supported rudder however, is inherently stronger, better protected from damage, and much less likely to be fouled by lines such as those on trap floats.
I was surprised to see, however, some shots I found of a salvage vessel from hurricane Irma, listed for sale in Florida. Those pictures DO show a strut from the keel to the bottom of the rudder! That one was listed as a 1988, and it has a Yanmar 4cyl engine.

Does anyone know if that boat was modified by it's owner, or did the later 27FC's all have that modification to their rudders?
Tom