Stack up and internal sortitude are pretty essential UI functions. Inventory management is not fun without them, especially without internal sortitude. I wasn't bothered by the cost of Internal Sortitude when it was first introduced becasue 30K iMG isn't a big deal on a character with a high level of skills and upgrades, but on my lvl 12 noob, the 30K iMG cost is breathtakingly expensive.
I really don't think these should even be upgrade cards, or if they are they should be like mappery, presented on the tutorial island. Being required to grind in order to get basic UI functions really isn't a good idea and not having bag-organizing skills really detracts from gameplay.