On the "facts" thing, the info I have is I guess technically hearsay.
In Daytona 2007/8 at the Friday night talk on Boas, Dave Barker gave a power point presentation on the anatomy of boas. He spoke about the reproductive tract and how it worked. He also stated that obese boas do not breed well because the fat in their bodies crowds out the internal organs giving no room for folicles and embryos to develop.
The following year the Friday night talk was on Blood pythons, this time Kara and Tracey Barker where the main speakers. They also commented on how obese females have higher instances of laying slugs for the same reasons outlined by Dave the previous year.
Now for me with the info given at those two symposiums coupled with info from vets about how to improve a female (insert animal here) reproductive health. I would say that fat females don't breed as well as females with proper body weight. (no matter if it is a ball, boa, lizard, dog, cat ect.....)
Would I call someone who power feeds a scumbag? No, I think that's a little extreme. However, I do believe that they are hurting the long term general and reproductive health of their animals. Which in turn will bite them in their wallet eventually.
To answer the question, yes I would buy a neonate or yearling since obesity can be fixed by dieting and if it is fixed young enough then their should be no long term effects on the animal (based on my knowledge of the subject).