Yes, ranged attacks from spells are typically considered to be "weapon-like". This is definitely true of rays (and almost all ranged touch attack spells are rays) since from the rules:
You aim a ray as if using a ranged weapon
The rules further clarify that rays function as weapons for several other purposes, and the FAQ makes this very explicit:
Do rays count as weapons for the purpose of spells and effects that affect weapons?
Yes [...] rays are treated as weapons, whether they're from spells, a monster ability, a class ability, or some other source
The same rule applies to weapon-like spells such as flame blade, mage's sword, and spiritual weapon--effects that affect weapons work on these spells.
Most ranged touch attacks which aren't rays are things like acid splash -- spells where you actually throw or aim a physical object. Those are even more "weapon-like" than rays, so it's probably simplest to say all ranged touch attacks work like this.
There's another FAQ that indicates you can take "Weapon Focus (ray)" and the like; strictly speaking I guess those wouldn't apply to orb spells like acid splash.
This is all following the precedent set by 3.5; in Complete Arcane it specifies that rays and touch attack spells are "weapon-like" and thus interact with feats in the same way that other weapons do, with a split between ranged/melee type spells.
The RAW doesn't specifically say.
As you note in your research, none of the rules related to hitting objects have any information about what to do if the object is attended.
That said, you can use existing rules to figure out a reasonable alternative. The rules for smashing an object that you link say:
An object's Armor Class is equal to 10 + its size modifier (see Table: Size and Armor Class of Objects) + its Dexterity modifier.
If you try to use the spell rusting grasp on someone's armor:
You may employ rusting grasp in combat with a successful melee touch attack. Rusting grasp used in this way instantaneously destroys 1d6 points of AC gained from metal armor (to the maximum amount of protection the armor offers) through corrosion.
You can similarly touch a weapon with rusting grasp:
Weapons in use by an opponent targeted by the spell are more difficult to grasp. You must succeed on a melee touch attack against the weapon. A metal weapon that is hit is destroyed. Striking at an opponent's weapon provokes an attack of opportunity. Also, you must touch the weapon and not the other way around.
It says that weapons are harder to grasp, but it doesn't actually give any rules for how you should determine the AC of the weapon.
With this in mind, one reasonable ruling would be to apply this rule to attacks against attended objects, but let the object use the attending character's Dex bonus instead of its own, as well as any other modifiers that the character has that apply to touch attacks, like deflection bonuses or a monk's Wisdom to AC. If you try to touch an attended weapon, you provoke an attack of opportunity. This means that it's a little bit harder to hit an object that a character is attending than it is to hit the character, since most objects are smaller than their users.
Another reasonable ruling would be to say that it's a Combat Maneuver, like any other. In this case, I'd say that touching an object that's being attended by another creature would work like Sunder. In this case, you'd simply make a CMB check against your opponent's CMD, provoking an AoO if you don't have Improved Sunder. The drawback of this approach is it means that it's basically impossible for casters to touch an object being attended by a creature except at very low levels, since the CMB of a caster goes up very slowly, but the CMD of most other creatures goes up very quickly.
Best Answer
Typically, only weapons and other attack forms that possess a range increment cause their users to suffer with those weapons and attack forms penalties on their ranged attack rolls due to the distance to the target. On Weapon Qualities provides this description of a weapon's Range entry:
If an attack form has no range increment, typically the attack form just doesn't suffer penalties due to range. It can be used against a target at its maximum range as easily as it can be used against an adjacent target.
For example, most spells have a Range entry in their descriptions. If the spell requires a ranged attack or a ranged touch attack, the spell suffers all the vagaries of it being a ranged attack. Launching a scorching ray at a foe engaged in melee against an ally, for instance, causes the caster to suffer a −4 penalty on the scorching ray attack roll. Further, the scorching ray spell (like most spells) can't extend beyond its Range entry, but because the scorching ray spell doesn't have a range increment, the caster can pick any applicable target within the spell's range and make the ranged touch attack needed by the scorching ray spell without suffering any penalties due to range.