Think of it this way - they're raising the typical trade value by approximately 20% over the current, so the +10% from Power Up will be equivalent to about 30% extra now (rather than the 40% that PUR members get)
If you think they won't still have trade promotions through the PUR website or the occasional promotion, you're insane, they'll just be fewer and farer in-between.
I foresee less opportunities for exploiting their trade in likes there are now. 2 weeks ago you could buy MGS: Ground Zeroes for $8.99 on the XB1 or PS4. With the current trade 2 PS4 or XB1 games for an extra $15, there was a potential to significantly increase your Gamestop credit ($11 for each with the PUR + an additional $15). I don't think opportunities like that will come around very often anymore.