Shiny Swablu question

Swablus spawn like pidgeys in my area, I've already evolved 3 including one crappy shiny. If you have a high spawn rate, go for it. Youll get that candy back in no time

I would wait for two reasons.

1. Even if the chances of finding a shiny one are low, you might still get a better one. Even if you want a shiny Altaria, there really don't need to hurry.

2. This is pure speculation, but when the next "Special research" thing comes out, it might have another task like the "evolve Magikarp" one and if so, maybe it will be "Evolve a Swablu" or "Evolve a Wailmer".
The next "Special research" might not come for some time and it might not have a task where you have to evolve something that requires 400 candy, but just to be safe I would save candies for that.
You do not want to evolve a Swablu today and end up needing 400 candies to do a task in a few days time. I know of a few who spent their Magikarp candy a day too soon and they were not happy ;)

You're not going to use Swablu in battle anyway, may as well evolve it now to get it in the dex. Even if you do get a better one after evolving this one it's not a big deal because there's no immediate use for an Altaria.

Maxed out my lvl 2 swablu. Pure trophy untill megas are the thing.