Pretty much, as it stands, All upgrades have to be paid for with real money. And a lot of it.

But why not at least have one upgrade requiring silver? or better yet-

Go the option of upgrading your crafting rank and add materials! This probably sounds crazy, but as someone who's played a lot of roguelikes I can say that what you carry over is important. And being able to upgrade without having to go through pay to win would really save the game in probably it's biggest flaw right now.

Pretty much it goes like this:
You want to upgrade your player inventory space once up to 40? 2000 silver, Thread, Cloth & Leather of whatever amounts. Still not satisfied? Upgrade up to 50 with 5000 silver, Thread, Enriched cloth & Enriched Leather. I don't know if player inventory upgrades only count for that specific character and therefore vanish once they die, but it'd be good to have a less wallet emptying method of upgrading it.

The same applies to the Vault, Legacy space and probably at least one crafting station with each having their own related items for the costs. The Vault could be Wood and Metal, The Legacy (Speak to the Bard) could be made from Amber & Obsidian and boss/"Rare" materials. The Crafting station could be made from the incredibly rare & costly "Core" materials such as Ember and Remniant that can only be obtained by deconstructing higher tier gear.

Heck, you could probably have it that you could upgrade various areas & vendors in the Tower to unlock various perks and whatnot.