I like the Auto Wah effect. It beats moving a pedal (or ribbon controller, etc.) every time I play a note. But when I hold a note down for a while, the note goes "wah - wah - wah ..." What I'd like is a Wah effect that goes "wah" only one time when I hit a note, even if I hold that note down for a long time.

The AUTO in the name "Auto Wah" is exactly why it goes "wah - wah - wah ...". Likewise, the PEDAL in the name "Pedal Wah" denotes you must manually apply the Wah effect with an FC7 pedal. And you'll be happy to know, the TOUCH in the name "Touch Wah" will apply the "Wah" only one time when you hit a note!

My mistake was that I thought (for no particularly good reason) that the "Touch" in "Touch Wah" referred to aftertouch. Aftertouch is of little use to me because of problems I have with my hands. This misconception led me to completely ignore Touch Wah.

So thanks for pointing me back in that direction.

I also finally figured out a valuable technique for getting the sound I want out of the available effects. I had been trying to set things in various ways, and a lot of the time I would change an effect control value and hear little to no resulting difference in the sound.

It turns out that the other 3 effects would often mask the changes I was making in the effect I was concentrating on. So what I do now is to work on one effect at a time by setting the other 3 to "Thru." Doing this has made things much more understandable for me.

The Touch Wah "scans" the input signal and applies the filter change according to its envelope. You can get fancy effects when you apply this to a drum beat :). It even works with the A/D inputs.
If you want to program a defined one shot "envelope" for your auto wah, independent from the input signal, there is another solution for that:
You can use the Pedal Wah effect and automate the "Pedal Control" parameter with the common LFO. The common LFO can be set to one shot and a custom waveform. There you can define up to 16 steps with values from -64 (full close) to 63 (full open). With that you can shape your desired envelope for your one shot Auto Wah. There also is a Slope parameter which you should set to up&down to avoid stepping. Try something like 6 steps, -64,63,32,0,-32,-64 for example and adjust the lfo speed. I suggest to leave "Key on Reset" at "1st-on".

Another solution could be to assign AS2 to "Pedal control",+32 in Ctrl Set and then use a user or preset arpeggio with controller data for Assign2 (Midi CC#17). Set hold to off and turn loop off in the Common Arp parameters. This gives you even finer control over the response of your Wah envelope and additionally you can turn off the arp and control the Wah with the Assign2 knob manually if you want.