I imagine it is certainly uncommon for the new, direct-only buyer but the type that are more educated to the nuances are probably far more likely to do it. If you are adding on 150 or less it probably doesn't make sense but for me, I split 300 into 125 (for the luggage)/75/50/50. I would show at an average of 75 even though its a discount for 300 @ $179pp.
There is a very fair point that resale restriction can drive purchases at non-restricted properties. The $179 direct is only worth it to me BECAUSE of resale restrictions on RIV and future. I'm never going on a cruise or trading out to any of the other bad point deals. I already get my discounts through an AP. They have stripped enough "perks" out of
DVC in general that the ONLY reason left to buy direct is resale restrictions on other resorts!