The only thing I can think of honestly, is the somewhat difficult time someone might have attempting to weaponize something like true love...
But that in itself should then be mentioned on the catches, as another modifier... Because as the rules go, it DOES gain a catch bonus, regardless of how difficult it may be to use... At the very least, as difficult as it is to weaponize, you could probably at least get a few Hundred people clever enough to find a way to do it. And while it may be difficult to find out about, there ARE other people, besides the ENTIRE families of White Court Vampires that know about their weaknesses. Its not at all comparable to the +0 example, of only one person alive in the world knowing about your weakness... And I'd say more, but I'm really making a poor argument... >.< Too tired to write as well as I'd like.. *sigh*
edit: and i mean, maybe even a small addition, stating that if the catch isn't really usable to attack the creature, and is mostly just for flavor, and a way to prevent the creature from feeding or something like that, then the catch won't provide any bonus.. something simple like that would be fine >.<