Have I missed any features? (Note, that I am considering the GNS 480 to be a
full Gamma 3, TSO C146 certified box, because Garmin will resolve the
current SAIB issue by the time I install the unit. So we don't need to go
through that discussion as part of this message thread.)

I'm not sure about the 430, but the 480 has 8 serial ports. One I'm
using for the remote transponder, another I'll use with a fuel flow
computer to be installed, such as the TrueFlow 500 from Insight. All
the Fuel Flow data can be displayed through the 480. Such as Gals/hour,
fuel to next waypoint, fuel remaining at destination, etc. without
having to use up any additional panel space.

The other serial ports can be used to connect up various barametric
hardware. Can't speak to 530/430, but the 480 has a lot of room to
expand.