Actually, if shooting in Adobe RGB matters, you've already dumbed it down a lot, because that means you're shooting JPG. If you're shooting RAW, color space is irrelevant - you can set it later.
You are right, I set mine to Adobe RGB but use raw, so it really made no difference. I use Lightroom 4 which has a prophoto gamut that is even wider.
I can do a soft proofing to my printer / paper profile and bring the colors into gamut as required.
You know, this has me thinking (a dangerous pasttime, I know...). I've often made the argument that the in-camera jpg settings do matter if you shoot RAW, indirectly, because the in-camera settings are applied to the JPG preview image that's reviewed on the LCD and used to generate the histograms. So, to the extent that you make exposure decisions based on the preview image, histograms, or blinking highlight alert, those JPG settings matter.
I wonder...what is the gamut of the camera's LCD, would sRGB vs. Adobe RGB make a difference in color channel saturation, a difference in the histogram or highlight alert calls, etc.?
I shoot RAW and use UniWB. Adobe RGB is important for those who use UniWB because sRGB shows inaccurate highlight clipping. For anything you could ever want to know about the histogram on the back of your camera, go to http://www.rawdigger.com/houtouse/beware-histogram
This quote below from the above link is what got me interested in UniWB, which is also explained by the article. (Minor thread hijack to follow...)"In standard (i.e. corresponding to the shooting conditions) white balance settings, the camera histogram and the camera overexposure indicator cannot be used to control overexposure."
For anyone who wants to skip the "why" and just try UniWB (like ETTR, but better), here is the quick and dirty. I don't claim to be a UniWB expert, and there are different ways to go about the process, but I have had excellent results with the following technique. (This only works for RAW shooting)
1. Cover the eyepiece and take a picture with lens cap on (I know what you're thinking) at the fastest shutter and smallest aperture.
2. Set your custom white balance to the picture you took in "1."
3. In picture style, set maximum saturation and max contrast
4. Set colorspace to Adobe RGB
Increase exposure compensation until you get blinking highlights, then backoff a third of a stop. The previews on the camera LCD will have a green cast and look terrible. Process in ACR and use Auto WB to get in the ballpark. YMMV, but I am a happy convert.