Here's one of the simple models I tried:
The FDV301N datasheet gives these numbers:
Input Capacitance (Ciss) = 9.5pFSo I sorta figured I'd see something in the 10pF to 20pF range. I wasn't too far off: including the Surfboard adapter, the FDV301N is a dead match for a 33pF NP0 capacitor. The Fairchild Spice model? It matches a 150pF capacitor pretty closely, with a few odd wiggles. In fact, if you pull apart the subcircuit definition you'll find these two lines:
Output Capacitance (Coss) = 6.0pF
Reverse Transfer Capacitance (Crss) = 1.3pF
Cgs 1 5x 78pI was a math major for a while, so I know this one: 78 + 75 = 153.
Cgdmax 7 4 75p
Running the same test on the bench with the DMN26D0UT showed it's a good match with a 22pF capacitor. The BSS83 has such low capacitances that it looked the same as not having a C1 in place. Apparently the 9.5pF of the scope probe and the various stray capacitances from the solderless breadboard are so high by comparison that you just can't see a difference. In fact, the scope trace looks the same whether the Surfboard carrying the BSS83 is plugged in or not.
While I was munching on leftovers for dinner, it occurred to me that the same mechanism could be used to get a crude measure of the input capacitance of a real circuit. As I mentioned before, the test above didn't include the Miller charges. So I rearranged things into a two-stage inverter chain. There's clearly a brief pause in the RC charge curve at the FET's threshold voltage, just as there should be, but otherwise it looks just like the test above. I'd guess it'd be safe to call it a 50pF equivalent at most. Certainly not 153pF, at least not in the circuits I'm going to be using.