I always do part points, part cash on my ressies. Part of my reason for doing this is that my vacations are always taken during the high point times of summer, spring break, and Christmas. I am staying in a one bedroom at BWV in a couple weeks for 5 nights, which "cost" me 150 points, but the other two nights "cost" 120 pts. I think that is outrageous, so I am paying $300 per night for those two nights. I save 120 pts for another complete vacation, and I only pay $600 for it. For me it's worth it. It's not a matter of not having the points available, because I do, but I just find the points needed to be too costly--I could rent those 120 pts for $1200, so I could make money if I wanted to.
I reserve the entire ressie on pts, then change when the rates for annual passport rates come out if they are available at my resort. Last Christmas I stayed the entire vacation on cash rather than points, because the ressie cost 375 pts, but I got the same accommodations for under $2000, and rented out some of my pts to off-set the cash. At Christmas, if you check in before Dec. 25 on cash, you get rates that are over 1/2 off for the whole time you are there. It works differently with points.