OK, fair enough. So why not encode to 29.97 in Vegas and avoid the re-compression in DVDA? To put it another way: What is the purpose of the MPEG-2 DVD Architect 24p NTSC widescreen template?

Ha! I learned something.
If you render using that template, DVDA will prepare 23.976 without recompression to a normal DVD folder. Even though that framerate doesn't show up in project properties (or the official spec). I just tested a short sample using the 24p template.
In that case the necessary pulldown is added at the player level because a flag is added in the encode.
http://www.custcenter.com/cgi-bin/sonypictures.cfg/php/enduser/std_adp.php?p_faqid=84&p_created=1043301600

Well, this is an interesting twist. Let me catch up with you: When you say that DVDA will prepare 23.976 to a DVD folder without recompression, do you mean that the VOB file will be 23.976?
What about the message I get when I go into the “Make DVD” process: “The video ‘(file name)’ on track 2 ‘Video’ in ‘(file name)’ will be recompressed”?
Plus, I ran a 24p render through the process and loaded the VOB file into the VLC player (since Vegas and DVDA won’t read VOBs). Under Media Information it says the file is 29.97.
Also, the document you hyperlinked seems to say that the “precise settings needed” to avoid recompression include a frame rate of 29.97.

I want to believe! But I’m not quite there yet.
Looking forward to your response.

1) Yes
2) Dunno. Are you rendering separate AC3 audio? Is your file too big? Are your project properties correct otherwise? Are you importing the media into the menu pane?
3) Maybe VLC is reading the flag. Reports 23.976 w/pulldown in MediaInfo.
4) Vegas will load VOB files.
5) Read the chart farther down. The ambiguity is why I ran the test.

This is getting good.

Indeed, Vegas does read VOBs (but it doesn’t recognize them as media files—another lesson learned), and it says my file is 23.976.
I discovered that chart a few days ago, and the “Suggested use” column at the bottom had me scratching my head.
The only sticking point is that recompress message. The sound is separate; the file is less than a minute; the project properties seem to be correct; I imported into the menu pane. When DVDA shows me the properties of the "Optimize" recompression, they include 29.97. Can I refuse the recompression? I’ll work on it.

Meanwhile, thank you for your insight. I knew there was something going on that no one had pinned down, and you got it. One last question: Why do we have to work so hard to get this information?

"The only sticking point is that recompress message."

If your file is the right size, and the right properties for the project, DVDA will not give you a recompress message. I tried it using Vegas Pro 8 with DVDA Pro 5.