Some things just need to be reworked in terms of prices..
Why mine gold, when I can fill up a barrel with masterfully prepared roasts and sell that for 20.000 dwarfbucks.
Why is a log worth 3 but a single wooden shield many times that?
Trading shouldn't be more challenging neccecerily, but definitely more balanced.
Value multipliers on items, either passively from the type of good or from the quality the end good was made, should become considerably less, especially when the end item is created at the end of an industry in which multiple quality modifiers come to play, leading to, for example, a pig tail fiber cloak worth almost 1000.
Instead of going anywhere from x1 to x12 on quality value modifiers, it should be a lot less, perhaps x1 to x3, meaning you will need a lot more items to make the same trade.
Some more usable exotic goods would also be nice. Nobody wants that elven wood armor, or the large human clothing, or blood barrels.. and that what is there, such as drinks, food, etc is priced relatively low and only a handfull of items can buy everything of those from the trader. Lifestock is rather cheap too, butchering them right away gives you a profit usually. Weapons and armor are often too low in quality to be useful either way. I can't make silver crossbows, or make high boots. The silver crossbows that dwarves bring have no quality or a low one, if they were masterfully made, my crossbow dwarfs would have a somewhat better hammer in close combat (I usually fight in the open field, so it was inevitable)
Craft, trinkets, other goods.
If these ever become useful to dwarfs, buying them from caravans actually becomes a decent idea. If a dwarf likes platinum and likes flutes, and you see a caravan sell a platinum flute, you could buy it. Sooner or later, that dwarf, or any other dwarf with no material preferene, takes it and gets a happy thought about their new item. After a while they would decay, or break in case of metals.
Children could possibly play with toys of their preference, and break them (perhaps even getting some tiny fraction of exp in a profession) giving a reason for those as well.
More dynamic prices, as also already said, would be an interesting idea. If a civ is able to bring me tonnes upon tonnes of food, and I trade it for my own prepared food, there should be a normal or slightly below average price, since they value my quality meals, but do have plenty of food to survive next winter. If they bring barely any food, or none at all, they might have some issues at home, and would likely be willing to pay more for your food, considering it will be worth even more when they sell that again.
When a major siege against a friendly city failed and there were many causalities on both sides, they may offer a decent price on ammunition, but not on weapons an armor, seeing as there is plenty of goblinite to go around with for them at the time, and not enough soldiers to wear it all.
When you asked for loads of armor in the previous year, they bring you loads of it. Not only would you be able to buy that, you could probably sell them metals and coal at higher prices, seeing as your request made them burn their supplies. Of course, if you now decide not to buy any of their armor, they will bring less of whatever you request next, because last time you ordered it and did not buy it.
Thats kinda what I imagine dynamic prices and scarcity could do