The issue is the pure endurance, but also versatility.
The party is more than high enough in levels to cast any of these spells directly, but there are so many different wands that the party couldn't cast each spell mentioned even once in a day.
So, with the wands, they'll have all that variety, plus all the spells they can cast directly.
I demonstrated once in this campaign that most spells, thrown spur of the moment, are a raindrop in a volcano when dealing with divisional level battles. That is, when your battle lines are a mile or more long and the fight is going to last all day, a 40 foot diameter flash of fire that's gone in an instant just doesn't mean much in the big picture.
Those same spells, timed and placed with a broader tactical view, can disrupt enemy efforts at key moments, and can turn the tide of a battle.
The main encounter will be such a confrontation. The "secret path" won't.
So my job, should they end up at this point (not a sure thing by any means) should be to get them to take the main battlefield and leave securing the secondary pass to an NPC force.
At the main battlefield they'll be facing an army with an arcane caster corps of its own. If the party accepts direction from the military commander, they'll be very effective, but they won't make many decisions for themselves and probably won't have much fun.
If they freelance they'll have more fun, but make less of a difference in the main battle.
If they mention the sheer bulk of wands they have, the commander will thank them for volunteering their arsenal, and their own army's caster corps will be far more potent.
They'll get back whatever survives the fight, and be paid for what was used of course, but... railroading them that way reeks of just arbitrarily taking their goodies away.
I think I'll do the unthinkable here: I'll trust my players not to go ape-spit on me, to see that they are indeed insanely over equipped and dispose of the excess in a responsible manner.
I'll just make sure that I provide them with ample opportunities to do that "reasonable and responsible" thing.