I'm not sure that's even a reliable rule of thumb.
We cruised in Februrary 2009. The deals offered during our sailing were exactly the same as what was being marketed to the public UNLESS you purchased something like 500 points. At that high level they added an RCI week to the offer. But for lower point add-ons the prices were exactly the same.
As the economy worsened in early '09 incentives continued getting better. But from June forward they have slowly pulled back on the discounts and now have an $8 price increase pending on BLT. Publicly
DVC insists its pleased with the pace of sales and the dwindling discounts seem to confirm that. While the prices we're seeing are not as good as they were in the winter and spring, I still think folks may be in for a rude awakening if they are holding out for similar deals.
Found below under "DVC Planning" , the thread is" "Questions for VGC Opening"
(Forgive me please, still learning the in's and out's of posting!

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#68
walter
DIS Veteran
Join Date: Oct 1999
Location: amherst,ny
Posts: 647
We were at the gathering last night also. The GV was amazing! I believe the hit of the night was the TV within the mirror of the master bath. One story that was told to me was an "A" actor is a big Disney fan and stayed with his family quite frequently at this resort in their favorite room. When the DVC addition started to be constructed, his favorite view became obstructed. So he called down to the desk to see what was going on and they stated that this addition was for DVC members. He wanted to know what that was and they transferred him to a sales rep. Low and behold he bought a substantial amount of points to guarantee his view (I heard approx. 3 x's a week's points). There are only two GV's at this resort.
When it comes to discounts, 14 months ago $8 per point was the norm and $12 was viewed as an amazing bonus. If DVC has its way, the days of offering a $20+ per point discount are quickly coming to an end.