Upload & Sell: Off
The point is moot because the buffer upgrades are no longer available, but some people use camera features that reduce the number of shots per buffer (e.g. long exposure noise reduction, perhaps lots of active d-lighting, certain jpg quality / ISO combinations, etc.) and might see a benefit. Slow CF cards would make a bigger buffer useful too because it takes more time to clear shots from buffer to card.
The D3s had the extra buffer space plus a lot of other advantages including sensor cleaning and better high-ISO performance. Might or might not be worth the extra cost to you, but was not so much extra when $500 had to be added to the D3 for the buffer upgrade.