This used to be one of the debuffs i'd try to land on 'boss' mobs before it got replaced with some enchanter debuff that was better. I honestly dont think the stat debuff portion of these spells makes any difference (str, dex, agi, ac, etc), but the melee / spell vulnerabilities do (see
Poison of the Brainbender)
I did notice a stacking issue that drove me to find a replacement for it, and I never posted about it because I hadn't planned on using Crippling Spasm in the long term. It had something to do with a debuff weapon augment I found in ssra that I briefly used on on a melee weapon. When the proc would go off I would get the "Crippling Spasm has worn off" message. I think it was
Trophy of the Snake.