Recently, after reading Dan's LAB book, most of my files spend some time in LAB to get maximum color variability.
Now, I'm wondering if my imaging has outgrown my colorspace, should I change to a wider gamut color space such as ProPhoto RGB?
Lab itself is a huge color space. It in fact is the largest in existence. Even though ProPhoto extends beyond Lab at a couple points it is still overall, smaller.
If you want to go to ProPhoto, then you also will be editing in 16-bit/channel mode. If you try to use ProPhoto in 8-bit/channel mode then you can actually degrade the image as you edit it. The reason for this is that a 8-bit/channel image does not contain enough information to describe all of ProPhoto and you could introduce noise and/or posterizeation.
Ah, you might be thinking to yourself, "Gee Dan, didn't you just say (er, type) that Lab is larger than ProPhoto? If that is the case wouldn't you run into the same issue with Lab as with ProP?" Why yes, yes you would. That is one of the problems with margoulis's theories on large color gamuts and high-bit editing.
I'm sure I opened a can of worms with that one, but so be it. Margolus (wrong spelling I'm sure) is wrong when it comes to those items and is easily disproved.
If you want to edit in ProPhoto (or even Lab) and properly utilize it, then 16-bit/challel images are in your future assuming the larger files and additional system power needed are not an issue. Otherwise AdobeRGB is as large as it is going to get in the 8-bit/channel world without running into unnecessary degradation.
I personally use ProPhoto all the time but your needs may not call for it. What are your needs in editing/printing?