One theme in my DF game is that I don't, or at least didn't, give out enough treasure. This is probably true overall, because I can be stingy for fear of giving away too much.
How much do they need?
First, they need to make a profit, because that's how I determine XP awards.
Upkeep costs in Dungeon Fantasy are $150/week, per PC. I have increased upkeep costs for people with appropriate disadvantages, like Compulsive Generosity or Compulsive Carousing or others that would have a steady additional cost.
Recharging Power Items isn't expensive, but neither is it cheap.
Potions that get used don't count against the trip's profits, but if you have to sink money into potions to ensure survival and success, you're going to spend a lot of money. Same with arrows, flasks of oil, rations, etc. - some of which do count for determining XP, but many of which don't.
Gear is really expensive in GURPS. You start with $1000, but a greatsword sets you back $900, a suit of plate several times that, and even light armor and weapons add up quickly. So a broken sword or rust-armor-rusted armor can cause a disastrous loss of money to an expedition that's barely making it by.
So they need a lot. $500+ per person per trip isn't a bad idea for a rough base. Higher is probably better, especially the more death they risk. If you're converting D&D module treasures to GURPS, you have to at least go with 1 gp = $1 and go up from there; 1 gp = 1 standard DF sp ($4) is better and you might want to go still higher as the money doesn't go as far. 1000 gp in AD&D split four ways is a solid profit for a trip for beginning adventurers. For DFers, $1000 split four ways barely covers the bar tab for a week, nevermind any incurred costs in expendables.
Whatever you think is enough, probably isn't.
I started low. A few thousand would be okay, right? Wrong. PCs were broke in no time, often coming back to town knowing they'd be broke before we convened game again. I dealt with that a few ones; the important one here is by increasing the amount of treasure.
Why more treasure?
They didn't find it all. A good portion of the treasure I put there was overlooked, missed, skipped over by mistake, not recognized as treasure, or left behind in the confusion. "Sorry guys, no one mentioned the chest of silver again after you opened it, so it's still back in the orc lair." That kind of stuff.
They kept stuff even when they needed the cash from selling it. Evil looking shield with a demon face on it? Plate armor of the evil cleric? That magic sword no one knows how to use? Those potions no one is willing to use? They held on to all of them. You can't expect them to cash in everything they can't use immediately, just because they need cash. My PCs held on to stuff they might need and borrowed money to eat.
(Although conversely, they'll often sell stuff you expected them to keep. Don't place stuff they need to continue the quest or they need to defeat a specific monster. Murphy's Law predicts instant sale.)
40 cents on the dollar. DF gives you 40% for sold gear. 100% for cash, gems, and jewelry, but 40% otherwise. So even if they do sell gear, they might not get much for it, and then they need to divide it up. My players found that armor and weapons made a good sale, but it wasn't a gold mine of profits.
It's a tough job. Multiple deaths to get this treasure, and regular severe risk of harm. For what? For a while it wasn't for enough. So I needed to up the treasure to justify this. Why would you go into a dark hole full of monsters for profit if there isn't much chance of a profit? That smacked too much of desperation and not enough of real fun.
Plus, the more money that comes out of the hole, the more intrigue that goes into getting it. Rival adventurers, say, or the fun of expanding the city's trade through sheer spending and demand. More money means bigger expeditions, more hirelings, more risk taking, and more crazy expenditures. The more they see come in, the more likely they are to spray it back out again.
Last session, the PCs took home about $5K each. That's much better than a dry hole for getting the players to risk their characters again and again.
So yeah, I learned I had to add treasure. My advice is, don't stint on it from the start like I did. Put in some cash and gems and jewelry, and give them a lot to blow it on. You won't regret it.