I finally found a google search combination that gave me some hints. I found a book titled "Why people buy things they don't need" by Pamela Danziger. Chapter 7 was included in the on-line review and included a small discussion on Art purchases. Among other data points, it has a chart that claims that in 2003 42 of households purchased art, prints or pictures in the 12 months prior to the survey. 2001 the figure was 27 percent and 2000 was 21 percent. Another chart indicates the order of purchases (by dollar amount anyway) was: Original Art, Framed Prints, Customed Framed work, and then unframed prints.
I'm not sure it helps but it's the first statistical data I've seen. So it's a start.
Also, here's a link to SouthwestArt readership demographics. SouthwestArt highlights original traditional Art so it's readership reflects that, but again, it's interesting to see some real data on this subject.
A "Unity Marketing" web page claims to have all the answers to these questions in their report, for a mere $2,500.
BTW, I asked this question in the Print Forum because I believe that taking pictures is only half the battle, the other half is trying to print our work in a way that reflects the original photo we captured and then worked so hard on. I assume that the ultimate goal of many of us in this forum is to sell our work, so that's why I posted it here.