[PvK]

Though I am no SC expert by any stretch (though I've killed a few), I think another way to agree with the thoughts so far is:

Point: Piling magic items on a good unit can make it even more powerful, giving it an even better chance of survival, and the ability to be superior to the most powerful opponents. Having a couple more items, or fortuitously-chosen items, can give your toughest warriors a major edge over your opponents. The investment can be more effective than recruiting more units without equipment.

Counter-point: Unexpected results occur, and there are counters, and the more piled on one unit is the more risked on one unit. There are some rather cheap items or summons which may defeat the best super-combatants more economically than the super-combatant was created for. The question then becomes, how much damage the SC can do before it runs afoul of a nemesis. A minor counterpoint is also, when an equipped SC falls, how many of his toys get captured by the enemy...

Some cheap things I've seen defeat equipped SC's:

alone:

Decay (spell, Banes, Bane lords, decay weapons, etc.)
Ethereal Crossbow
Soul Slay
Disintegrate
Poison
Trampling
The Stone Sword

with help from friends:

Entanglement (Tangle Vines, Vine Arrow, Vine Bow, etc.)
Curse
Flame Arrows
Horrors
Vengeance of the Dead
Black Bow of Botulf
Herald Lance
Fatigue (see strong cold or heat auras)