In college, I took a research methods course and about 1/3 of the semester was spent on surveys. I took the course about a year ago, but the thing that stuck with me about surveys is that they are incredibly effective, but it all depends on how you administer them. We were instructed to shy away from mass mailings, because unless you`re the Census Bureau, the response rate is generally low compared to the relatively high cost of distributing them (especially given the recent increase in postage). If you are going to conduct a survey though, I would focus on a particular demographic (like DipLady suggested) and include a brief introductory paragraph that makes people think they were chosen exclusively to participate. Make it exciting and personal. I know I have seen other posts on here too about determining interest and market research, so you might find some helpful tips if you poke around a bit.
I would have to agree with Nikole. I think Tuesdays would be good, or perhaps Wednesdays - I read a study somewhere suggesting that Wednesdays were the most productive day of the week. I think people will be too busy on Mondays trying to catch up from their weekends and getting their coming week organized to try and introduce anything else into their schedule. The same argument may be true for Wednesdays as well...
I would tend to agree with Craig and Andy. The homepage definitely needs some work, and the pages each took a really long time to load (not sure if that`s a site issue for you, or a browser issue for me - although every other site seems to be fine on my system). Also, I would move the BACK and NEXT buttons somewhere else - either right below the images or above them... or just somewhere more visible. The first time I looked at the site, I missed them completely and didn`t see anything more than the first page of merchandise.
Your site is absolutely beautiful! It`s very simple and elegant - as are the cards and wall art. Very impressive. I don`t think you need to add a larger view of the cards; if you click on them, a larger view and description pop up, which works very well.