For small amounts, short answer would be no. If you want to see a large wholesale market in one of their farming towns, then yes for the experience. In general, farming towns do not have much in terms of attraction. I would not bother. If you go to Shanghai there are plenty of sights in the surrounding Jiangnan area which does not involve quite as much travelling. Hangzhou and Suzhou are famous for their history, with ancient buildings, canals and scenery. They have their own wholesale markets with pearls but are mainly tourist traps.
In Shanghai you can there is a pearl market in Nanjing Road, the Pearl Circle near Chenghuang Temple and corner of Yan'an Road and Hongmei Road. I forget their exact names, but the cab drivers should know. Prices aren't always the same across the board. The third is generally cheaper as fewer tourists go there for pearls and there are other wholesalers in the same buildings, from clothes to shoes and accessories. I got a 9mm AAA deep lavender for about US$250 (current exchange rate - it was probably US$200 when I bought it). If you want off round that would be a grade or two down so it's half the price for every grade down. I even got a small 6-7mm off round pink exotic strand for around US$50 back then. I went in the off-peak season so they were eager to make sales.
The Chinese customs don't generally care what you take out as long as it's not huge amounts of RMB (I think the limit is RMB20000). They love for you to take as many trinkets with you as possible. Customs in your own country would be a greater issue.
Aspiring ninja. Go Storm Shadow!