Here's a good general info website: http://www.b737.org.uk/
The winglets actually decrease drag by decreasing the wingtip voticies. There is some consideration being given to winglets for the -600 but there isn't any demand as the plane is considered a bare-bones, short haul, small load economy version of the plane.
One more thing, the winglets were created to make the BBJ
more visually appealing. They all have them unless specifically eliminated by the customer.
Boeing (as a group) was surprised and continues to be surprised by the economy figures as the database is built.
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533