The raw file is my master; I save my raw files and revisit them when I need a different-sized print.
Its not the workflow I'd use....
Raw files are not what I'd consider masters (they are Raw, need to be rendered even if you print within the Raw module).
In that situation, is there any advantage to setting your Workflow Options to a color space with a wider gamut than sRGB, saving as jpg through Camera Raw in that wider space, then converting to sRGB for the print?
Yes, you can always move from a wider gamut to smaller gamut just as you can always move from a 50mb file to a 5mb file. But going the other way doesn't work. Also, as I tried to point out, once you render the data into a working space, that's locked in stone in terms of moving to a wider gamut and you now begin to bake in pixel edits.
I assume if there is no clipping in sRGB, there would be no advantage.
How do you know there's no clipping (at least in Lightroom)? In ACR, the histogram does indicate clipping based on the currently set encoding color space.
Then there's the possibility that this lower gamut data might be pasted into a wider gamut document (if you're compositing). So you don't want to go sRGB to ProPhoto if possible.
I wouldn't be super concerned with clipping at this point in the workflow. You're going to clip anyway going to an output color space (be it your web page in sRGB or to some printer color space). If you had to work with an 8-bit file, that be one reason not to work with a very large gamut working space, otherwise, its simply a big container for whatever you decide you want to encode into that container.
Considering that at least in Adobe Raw products, you're always processing in ProPhoto RGB, even if your data could fit into sRGB, I'd make life simple and encode in ProPhoto RGB and convert later to a desired color space for the needs at hand. That's true with rendered images too. If you import an sRGB document into ACR or LR and do any edits, that data ends up in ProPhoto RGB linear TRC.