I would definitely go back for the white betta

I saw a white one yesterday that I almost got, but 2 bettas in 2 days is too much. Even if it was my birthday!
Wow 28 would be a lot of waterchanging! The way I think about it is as long as you have the room and the time, whatever number of bettas you get will be way better in the hands of someone willing to care for them than somebody that just has just one that will die from lack of interest.
An update on Mimpi: He ended his hungerstrike today on freeze-dried bloodworms(I offered him frozen yesterday and the booger refused them). Also, I saw him flare for the first time! He stopped doing it when I grabbed the camera, but here's a picture that's close.