Keep in mind that if you buy a totally different use year (via resale, since Disney won't sell you a different use year), is that they become two totally different contracts. Points cannot be combined in any way for making reservations or to determine banking amounts.
The two contracts would be as separate from each other as your current contract is totally separate from mine.
Finally Use Year doesn't really mean anything if you don't cancel your reservations. It only comes into play if you cancel a reservation and the points are returned to your account but it is too late to bank them.
You do realize, I hope, that if you purchase points at BWV, only those points can be used to make a reservation at 8-11 months ahead. You could not use the OKW points for that BWV vacation until the 7-month point. So if your purpose is to have BWV as a home resort, be sure you understand this.