Another thought:

Is there a price difference in either direction for miles or cash? i.e. if one direction prices out at 2/3 the cash price, you could redeem miles in only that direction, paying cash for the cheaper direction.

For example: If the fare is $430 in one direction, but $200 in the other, and mileage redemption is 25K in each direction, it may be best to pay the $200 cash for one direction and 25K miles for the other.