The cost of redeeming Voyager miles depends solely on what the Voyager programme dictates - the United programme's redemption increase has no bearing on this.

Apart from roadwarrier's sensible comments below, it usually makes sense to build your relationship with the airline you fly most. Having said that, there are other considerations especially with regard to your *A status.

Not sure of you have status with Voyager (it sounds as if you would, given your mileage earned). Starting afresh with United Mileage Plus will mean building your status from scratch. But you would keep your *A status via Voyager until the end of the calendar year in which it expires - so timing the move can be important.

Another consideration: try to avoid having orphan miles in your Voyager account - i.e. too few miles left eventually to make a redemption. It may be beneficial to still throw some earnings to Voyager in order to use up the remaining balance before they expire.