Agreed about the upgrades. The only one that makes a bit of a difference is the garden. The Chantry garden opens a war table mission to collect tithes and the herb garden allows you to plant and collect more herbs. Other than that, the rest is purely cosmetic, which would be fine if the rest of the castle got fixed along the way. Those crumbling walls are just an eyesore.
Honestly, I don't really mind the fact that most of it is cosmetic. But it would be nice if it was used for NPC interactions. Let's say you pick the chantry garden - have more sisters standing there, teaching and preaching, have groups of NPC come by to kneel at the statue and say their prayers. On the other hand, if you pick the alternative, have more pots standing around, plant more plants - make it a cozy place where lovers would go or where friends would sit and talk in peace. Where scholar would discuss the plants.
Just make it mean something.
It would have been nice if there were more upgrades though. I really miss a bit more customization to my castle. And it would have been nice to see some interaction with the present characters. So - have Solas stroll the gardens, and Cullen walk through the Templar Tower or Vivienne through the mages tower.
And I agree with what's been said before - why is there still so much ruin left over? We run around, invest, collect - and yet there are still dozens of areas that are crumbled.
And yes - PLEASE ADD SOME STORAGE. Why am I master of an entire castle and there is not a single box where I can put some stuff in? Really?