Given that it is an evolved adaptation, I would generally agree that it is entirely possible the adaptation has some significance in terms of a survival advantage, other than the typical purpose of general armor to discourage predators.
I do believe that aside from protection, spines do have some sheltering effect against the sun's rays. I wouldn't know if spines that are bent at the end would be more efficient in such a purpose.
What I do know, is what I found doing a quick search, and then reading about the "fishhook cactus", whereby: "seeds germinate in areas where water movement occurs or in areas where standing water accumulates for some period of time, and during flash floods, the hooked spines allow the plants to be caught on water borne debris and be uprooted and carried to areas where water tends to accumulate." I would expect that if small creatures could be caught and trapped, that that would not be the purpose of the spines, but rather, an unfortunate and "unintended" side-effect. I suppose that hitching a ride on an animal could be an alternate form of transportation, but doesn't make much sense because the ultimate destination would be completely unpredictable and could result in the plant being transported to a place it can't survive anyway. That wouldn't be much of a survival strategy in my opinion. The transport by flash flood on the other hand makes a great deal of sense, with transportation to an alternate location where presumably water would collect or stand for at least some useful period of time.
Unless someone can show evidence that these cacti are actually carnivorous
, I can only scoff at the idea that the purpose of the spines is to actually trap and kill small animals.
