I am the one with the wobbly pup, Weebles so I thought I would give my 2 cents.
First off, I see what you are saying. I am passionate about spay/neuter and educating people about s/n and I know that the reason millions of animals die in shelters is because people don't spay/neuter. I've paid for many animals to be fixed, I work at a s/n clinic, and serve on the board for the shelter so I can definitely see where you are coming from.
With that said, Weebles is absolutely worth helping (and most people who meet him would agree). I see no reason to euthanize a perfectly happy puppy who brings so much joy to our lives. It's difficult to draw the line when you are emotionally invested in an animal. Looking in as outsider, it's probably easier to look at the big picture.
But I feel that our situation is a bit different. The shelter is not spending a lot of money on this puppy. The shelter could not afford to spend a lot of money on this puppy. We are able to afford a wheelchair for him because someone heard his story and donated the money FOR him. She never would have donated to the shelter...she isn't in Iowa, she's in NYC and never heard of our shelter until she heard about Weebles. Weebles' story touched her heart and that is why she donated. So to this person his life is worth it...and that is how she chose to spend her money, bless her heart! This donation might not make a huge difference in the big scheme of things, but it'll make a huge difference to Weebles and the people that love him. It's similar to the starfish story I guess.
If a shelter, rescue group, or even an individual chooses to spend a lot of funds or resources to help one animal then I think that is up to them where to draw the line. Everyone has different priorities when it comes to causes they believe in.
I love the story that was posted about the handicapped puppy!