You misunderstand. Blessings are essentially a temporary separate favour "item". So you can get one along with any favour item you might own.
I guess the free part doesn't work well. So how about we up the cost to 25 or 50 points? Assuming you lose the game you still make a net profit, or no profit. Both of which help curb the buildup of useless favor. The better blessings would cost far more, you would only break even if you did exceptionally well.
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Heres another idea. Instead of making blessings just another kind of favor item. How about making them conditional? Say you can only get X blessing if you kill 5 demigods in a row. On the flipside you could LOSE blessings if you fail at certain things.
So for example you get the "cheap" blessing from the god of wealth. This results in a small bonus to gold gained through fighting. After gaining X number of gold without spending any you can drop more favour for an even bigger bonus. The catch is that you LOSE the bonus if you spend too much of that gold.