Do you plan to fly WN again any time in the near future?

If so, then use the gift card before it expires so you don't lose it, then pay the extra funds (if any). You'll get the points that you can use later.

If you're not planning to fly again soon, use up the points you have. If the gift card expires, you'll just have to eat it.

I don't know of any way to combine points and cash/gift card/ LUV vouchers on the same ticket.