Regarding gold, I like that it has weight in DF because there are game systems specifically designed to allow the player to cope with vast wealth. The bank accounts and letters of credit. If gold is worthless then they may as well be removed from the game as there would be no reason to go to the bank except to buy a boat/house or get a loan (robbing the bank!). The question is whether the need find and visit a bank to convert gold is too onerous that it becomes a chore / annoyance rather than an immersive action. This is the exact reason I allowed gold to be dropped into the wagon... then you can convert it when you wish to do so. Hopefully this keeps the atmosphere of the mechanics, while also not making a player do boring crap when they don't want to.
I would agree for most games where all it does it govern the number of (zero consequence) trips to local town/shops. However in DF with the dungeons that reset when you leave, you need to pick and choose what you pick up depending on how many trips you want to make back to entrance so you can toss it in wagon. You can't simply just hoover loot until is all gone because the dungeon resets when you leave, so I think it's much more meaningful in DF than most games.On the other hand, I agree with you about encumbrance, it's mostly a busywork feature that makes the player spend time micromanaging without really making the game more difficult, just more tedious.
