I would like to recommend that purchased upgrades go to the bottom of the list, so the cheapest upgrades you haven't got yet are always the first items you will see on entering that tab, reducing the need for scrolling.
If this isn't the active tab, I've noticed that when I return to the tab, the PP has dropped significantly, despite being able to increase easily as the active tab.
Great idea! We're also looking into a "Purchase all" button that grabs all the available upgrades you can afford.