I think what we need and maybe Adobe will include this at some-point in their development of LR or ACR is the ability to preview or predetermine the image colour gamut. The user then could select the appropriate colour space dependent on the image colour gamut if so desired.
The image is in XYZ at some point in the pipeline so a quick subsampling to LAB for gamut comparison would be quite straight forward.
For example if an image contains a very small colour gamut would it need to be rendered to prophoto or would sRGB suffice? or vice versa.
I don't know what type of tool you would like to have, but both ACR and LR have the capability to determine if the gamut of the image fits into a selected color space for the final rendered image. In ACR you can set the preference to render into sRGB. If gamut clipping is apparent as in the histogram of the first image below, select AdobeRGB or ProPhotoRGB to eliminate the saturation clipping.
In LR, the rendering into the selected color space is deferred until the export stage. One can use soft proofing to see if there is clipping when exporting into the final color space as shown in the second image below.
Either way I think it is important to match as best as possible image gamut space to rendered colour space.
If you use 16 bits per pixel, I see no disadvantage in using ProPhotoRGB. If 8 bit output is desired, then a smaller space would be preferable. Personally, I would not take the trouble to go through dozens of images, selecting the appropriate space for each, but would simply use ProPhoto as Jeff recommends. Otherwise, you could use a space that contains the real world surface colors that occur in nature. The size of such a space is shown in the third image below, courtesy of Gernot Hoffmann
. Bruce Lindbloom's BetaRGB might fit the bill.