I must be forced to agree with noelberg there--this is no place to disrespect guppies, even if you do find them to be rather small, insignificant fish. I myself have not only raised the illustrious Cobra guppy as well as many other livebearers, but I have, in fact, used guppies as feeder fish in the past. Mind you, these were the common 5 cent kind meant for such purposes, but on the whole, I believe that guppies are good for either showing or feeding to other fish, as long as you are not using guppies such as the above-mentioned Cobra for such a purpose. So, I do indeed agree that guppies can be feeders--however, I also agree with the rest that the more elegant kinds of these fish do, indeed, have their place in the world of livebearers.
By the way, I myself fully dislike the notion of killing these fish as well--however, when I bought the feeder guppies, I believed at that point in time that I had no other option. You see, I had found two large green frog tadpoles mistakenly placed in feeder fish aquariums, and, fearing that they may not survive for long in such an environment (and with every intention of releasing them back in the wild come spring) I bought them. However, they not only speedily grew arms and legs, but they grew mouths as well--mouths no longer meant for the purpose of eating algae. Not knowing what they would eat or how long it would take for them to completely metamorphasize into frogs, I bought the guppies for them. And, believe it or not, the majority of those guppies are still alive. I found out that no, actually, green frogs do not like to eat fish, and hence those fish are still in their aquarium to this day--only, they have most certainly multiplied greatly in number, so it appears that I have a small colony of these fish now.
Considering the fact that too many of these guppies can increase the ammonia levels too much and hurt the frogs as well as the fact that I need a way to cull the fry that I get from my other livebearers, I am, in fact, beginning to think about buying a nice, predaceous fish that will actually eat them...
By the way, about the Endlers--I too was able to get one, and he is now desperately enfatuated with my huge female swordtail that is many times his size. I even put in two female guppies for him so that perhaps the swordtail could get a break, but he ignores them entirely...he is an extremely odd fish when it comes to his "tastes."
You obviously don't get it do you.. 
??? 
