Yesterday I suggested figuring out how much delvers need for a trip to be profitable. Enough to get by plus enough to incrementally work towards upgrades and training, that is.
Basically establish the cost of doing business for adventuring so you can decide what's enough to put out there for them to find.
A commenter on my Google Plus stream suggested throwing out the whole "how much do they need" and just calibrating what they spend it on. That's not a bad idea starting from scratch, but I already have a very well developed system of costs/rewards for the money. It's easy to add to it but not to rescale it if I suddenly handed out 10x as much treasure and just wanted to change how it affects them when spent. But it's not a bad idea at all.
Now that you've got a number in mind - cost x delvers - you can place away.
Here is what I've learned.
You need to put in a multiple of that. - If delvers need X treasure each, and you have 6 delvers, putting in 6x isn't enough. Not unless it's sitting in neatly stacked piles of coins on the floor in the middle of an easily-located room.
You need to put in extra, a buffer, to give them a range of anything from 0x (we found nothing! This dungeon sucks!) up to at least 12x or more.
They won't find it all. This is less true in smaller "one-trip" dungeons than in megadungeons, but it's true. They won't find it all. They won't look up and see the chest on the ledge. They won't check that one closet where the fur coats and hanging. They might not check for a false bottom in that chest or look under the altar or fish around in the pool of green slime.
Some might get bypassed or destroyed. They might just have to skip the dragon's hoard because they're too beat up to take him on. They'll possibly throw fire spells into the room full of ransomable prisoners not realizing it's not entirely full of orcs.
Some won't fetch full value. One classic mistake I used to make was putting in, say, $500 (in GURPS) or 500 gp (AD&D) worth of salable stuff in to a hoard, and then letting the PCs sell it . . . for a percentage of that. Say, used goods, Balto gives you half price. So my 500 gp worth of stuff was really 250 gp, tops.
So if you place by value, remember to consider what the actual sale value will really be. This can hit you both ways - in GURPS, a skilled or well-connected (aka Wealthy) seller can push the price up to more than double the expected value. You need to be aware that if you give them 500 worth of gear they might get as little as 250 for it or as much as 500+ for it. Plan for the low end, if you're concerned they might walk away with too little.
They'll keep some of it. My players do this very, very often. So much so, that I checked one character who was perpetually broke and found he had north of $25,000 worth of gear. Starting money is $1,000. How did this happen? He kept a magical shield, the most valuable jewelry found so far for a power item, and filled up on better gear.
You may put in an ornate suit of really demonic-looking plate armor and have the cleric decide to keep it. ("The Good God doesn't mind me looking badass.") That can drop the haul from "enough to make a living and pay the rent" to "Do you think you can let me slide?" in no time, even if they got something more costly than they could afford. It's happened in a few of my sessions that they took home real, true wealth, but didn't turn it into money.
Note, however, the reverse will happen. They'll sell the armor you placed, sell the would-be-valuable-later meteoric weapon, convert the potions into cash, etc. with exactly the stuff you most expected them to keep. You get to play god but it's their game too, and you can't force them to keep stuff without lots of unpleasantness. My suggestion? Let them buy it back when it turns out they need it.
Adventuring can get you killed. Or cursed. Or crippled. Or possessed by demons. So it's quite possible some of the "profits" will go right into "unexpected one-time charge" because of a bad roll or a poor decision.
This also means some treasure will be bypassed because of fear or certain of death. A party badly weakened by previous encounters might need to head home, not head for more loot. So you can't bank on them finding everything, if only because the monsters and traps attach a cost to the treasure.
All of that is why I think you want to put at least double the treasure you want them to end up with - they'll never get all of it, or realize the value of all of it. There needs to be extra. How much extra is probably another post . . .