Well, I haven't been the DM for 15 levels. It's been a group exercise.
Here are relatively common spells they don't use:
Blur - Gives 20% miss chance, regardless of the enemy's attack bonus.
Displacement - Gives 50% miss chance, regardless of enemy's attack bonus.
Detect Evil - Gives you a clue who/what you're dealing with.
See Invisible - No comment necessary.
Mirror Image - Variable miss chance.
Shield - Adds 4 points of AC, stops
Magic Missile spells
False Life - Lets the spell bleed so you don't have to.
Their offensive spell list is as follows:
Fireball
Scorching Ray
Lightning Bolt
Magic Missile
Ice Storm
and rarely
... Cone of Cold
That's about it. I focus on the spells because we don't have a real Fighter type,nor a real Rogue. We have exactly one character in the party who isn't a spell caster.
One of them wasted precious action-round time trying to cast
Doom on some Giant Scorpion. A 1st level mind-affecting spell that gives the enemy a -1 to hit, wasted on a Vermin type that's immune anyway, even if it couldn't make the Save in its sleep.
And the Druid still loves to try
Entangle, even when he's in places where there really isn't any plant life for it to utilize.
Now, this past week I more or less convinced them that
Hero's Feast is a good idea. Up until now the Cleric had only cast it as a special treat for some favored NPC. Even after I told them that pretty much all the African tribes used poison on their weapons, they missed the clue. Even after their Healer got poisoned by monstrous scorpion, they missed the clue. Even after they saw their guide saving the poison from one of the scorpion, for his own uses, they missed the clue. They would have walked into the Colossal Monstrous Scorpion (DC 33 poison save, D10 of Con damage) if I hadn't had some bad guys work to get their NPC/Cohort Bard addicted to something nasty. That convinced them that the poison immunity was worthwhile, even if it is only for 12 hours, and hence wouldn't have protected their Bard (Drugs were slipped into his evening meals).
The Colossal scorpion I mentioned did waste an attack slaughtering one of their draft-camel. I also reminded them that they could use
Shrink Item on water barrels or chests of supplies. Maybe now they'll abandon that stupid cart and start moving faster than 15 overland.
They also realized (maybe) that the Druid's
Transport via Plants could take them to the waterhole nearest their goal all in one shot. They'd only been thinking of it as having a 4 creature limit because they had an amulet that could do it with that limit once per day. So we'll see if they decide to shortcut several weeks of desert encounters.
They did manage to knock out one of the enemy conspiracy, a member of the Illumian Cabal that they've been chasing and never getting close to.
Their next action? The Druid arrived first in bird form, changed to Human, and executed the unconscious man. I gave the Barb/Wiz (ostensible party leader) the opportunity to
Message the Druid with advice. He did, and his advice was, "Do a good job on him!"
So they lost a (so far) unique information opportunity. Just threw it away. I wanted to cry.
To be honest, I'm starting to think that they deserve to fail on this mission.
We'll see if the survive my next encounter. Specifically, we'll see if anybody remembers the Stone Salve I provided, or thinks to throw
Death Ward before messing with the undead, or the Giants. (Oddly, the undead I'm using are the ones who petrify, and the giants are the ones with the death magic. Kind of a reversal.)
I have a couple of sets of ruins for them to waste time in, and the requisite Mummy as well. (It wouldn't be a Sahara adventure without Pyramids, ruins and a Mummy or two, now would it?

)