I have enjoyed reading this thread!
My entirely non-expert opinion -
I think artistic expression should be considered as a great window into various factors that we list when we talk about intelligence and giftedness.
At a very young age -
Level of detail - surely speaks volumes about memory, and as has been noted here, may even be an indicator of understanding of human culture and interaction!
Drive to create - how often does the child draw, sing, etc., with what level of focus - a great guage of overall intensity and ability to focus - even though other subjects may make them act out and seem incapable of focusing (personal experience on that one!)
For somewhat older children I have seen more specific artistic milestones listed on a website or two which I think are of interest. (recalling from memory here) Use of skills such as foreshortening, attempting to render 3-dimensionality of an object, composing with use of foreground, background (mid-ground). Shading, etc. I think I have read that these can be good indicators of visual spatial ability, and more of the above traits, since level of detail & focus are increased.
If you are seeing amazing things artistically from your child and have not considered intellectual giftedness - it may be time to rethink. Also, I know I have said this before, when we were applying to the gt proram at school for my ds, bringing in drawings really helped flesh out what he was capable of and what is going on in his head.
