With the PE basic too you can pay the difference to the next level in PE and then use the miles to upgrade to business. But if you do not have IML then I see no point in paying for the higher fare as the only difference would be that you have to pay for the seat selection. Depending on the sectors you fly it is not worth to pay an higher fares for the PE instead of the basic fare. It is the same cabin and boarding is the same queue and everything remains the same.