Speeding up learning is a fools errand. You'll learn that stuff soon enough anyway. No need to rush it.
Frankly I consider shrines and donation to represent a huge flaw in the game. Once you've gotten on, much of the end game is "make stuff and throw it away in fancy garbage cans", which is not all that much different from "dig a ditch and then fill it up." One would expect a bit more.
have you collected 11 of each emblem to make an icon of each giant.
I'm on my 2nd set to have on my street instead of in my house. There are achievements to get for I think getting 151 emblems too.
Speeding up skills can be worth your time when you have 70 days to finish mining 5 like me. Making emblems and icons are fun too, 11 icons means around 2500 bonus img, 5000 bonus energy, 5000 bonus mood (for me).
Lastly, the img you got from donating is big, and img can be used for valuable cards.
Ultimately favor is just a side-effect of donating to shrines for iMG.
There's not enough to do with the emblems since after you have learned all the skills there's no way to avoid getting more emblems, and after you've made a set of icons they just pile up.