Pay to choose seats now

Booked 2 World Traveller Plus tickets from Boston to Heathrow.....daytime flight. Wasn't planning on paying to book seats in advance. Checked today and there are about 10 seats left. All remaining seats are middle seats in the center row with the exception of 1 aisle seat. Should I pay to book that aisle seat and the one next to it? otherwise we will both be in middle seats. Thoughts? The seats would be $67 each.