On the detrimental side you have to cart the winglets up to that altitude first, and each weighs in at a couple of hundred kilos.
Yes, they aren't fitted to the -D's due to minimal time in cruise on the JAL/ANA domestic sectors however, they're really not heavy at all. My airline has a habit of damaging -400 winglets on a fairly regular basis and they're very light and easy to get on and off - they're mainly made from fibreglass. An easy two person job.
From the Maintenance Manual:
Winglet
The Winglet is a drag reducing component which attaches to the
Wing Tip Extension at two fittings with three bolts. The construction
of the Winglet follows standard airfoil practices using a structure of
spars and ribs enclosed by skin. The majority of the Winglet Skin is
made of composite material except for the Leading Edge and Tip
which uses sheet aluminum. The Winglet is faired into the Wing Tip
Extension with three fairings and weighs about 146 lbs.
That's around 65 - 70 KGS